Winning, Losing, and Drawing
How do you win a game? How do you win a tournament? There are a number of ways to win or lose. And there are also draws.
Winning a Chess Tournament
What's a win worth? How is chess scored in a tournament? Usually a win is 1 point for you, a loss is 0 points for you, and a draw is half a point to both players (so a draw is "splitting the point"). Occasionally, some fancy advanced tournaments use different scoring of 3-1-0 to discourage draws, but that's uncommon; the system that's the most common by far is 1 for win, 0 for loss, half point for a draw.
How to win a tournament? Well, basically you have to win as many games as you can! And half-point draws also help. In a tournament everyone usually plays the same number of games, and whoever has the most "points" from wins (or draws), beats players with less points. Often there are different levels or divisions (e.g. by age groups, or by abilities/ratings), so you might not have to beat all the people, but only those in your division.
Winning or Losing a Chess Game
Winning by checkmate: The basic way to win is to give checkmate to the enemy King. The King must (a) be in check, and (b) there are no legal moves. There is no need to play the next move and actually capture the King.
There is no "double checkmate"! Sometimes you give checkmate and your opponent is just about to give checkmate on the next move. It doesn't matter, whoever checkmates first wins. The other player cannot still make their next move and claim "double checkmate" or a draw or anything else silly. First to checkmate is the winner. The game stops immediately.
Winning (or losing) by adjudication: In a lot of beginner tournaments, if your game doesn't finish by the end of allowed time, an official adjudicator will look at your position and determine a winner & loser, or declare a draw. There is a lot of factors used to determine who's winning a game, but one of the most common is where someone has a lot more pieces than the other player. An adjudicator will often consider the "material balance" (e.g. Queens are 9, Rooks are 5, Bishops/Knights are 3, and Pawns are 1).
Resigning: When you "resign" in chess, it means that you give up or concede defeat. You are allowed to resign in many tournaments. If you are three Queens down, you don't have to wait for your opponent to checkmate you. You can just say "I resign" and offer your hand for a hand-shake. There are several other ways to indicate that you resign, such as turning your King onto its side. On the other hand, if your opponent has 3 Queens, they're quite likely to stalemate you, which means you escape with a draw!) Also, resigning has to be clear too, for example, if your opponent just offers their hand with a mumble, are you sure if they resigning or offering a draw?
Winning by King Capture (Lightning Chess): Some forms of chess, typically rapid play chess or "lightning" chess (5-minute chess), you can take the opponent's king. For this to occur, an illegal move must have been played. And note that where a King capture is a win, it doesn't matter if the other King can be taken. There is no "double-king-capture"; the game ends as soon as one of the Kings is captured.
Winning by Claiming Illegal Move: In most tournaments, a player making an illegal move must simply play a different move. But in some formats, you can claim a win simply due to an "illegal move" by the opponent.
Losing on Time: Some chess games are timed by a "chess clock". If a player runs out of time, they have "lost on time". It's also sometimes called "forfeiting" on time. In most tournaments, it's not an automatic loss, but a player has to "claim" the win on time. If you notice that your opponent has lost on time, you will have to stop the clocks and claim a win on time. (Note that in some tournaments, if both players have run out of time, it is a draw regardless of who claims it. So you'll have to claim a win on time before your own clock runs out of time! There are also sometimes obscure rules whereby a person cannot lose on time and only draws if their opponent doesn't have enough material to checkmate them.)
Losing on Time by Being Late: Some tournaments will forfeit you on time if you are too late to the start of the game. Sometimes this is called the "grace period". It is often 30 minutes or 60 minutes in long-form tournament games.
Draw by stalemate: It is an odd rule that often seems very unfair, but stalemate is a draw rather than a win. If your opponent cannot make any legal move, and they are not in check, they are in stalemate. If they were in check, it would be checkmate, but without that check, it's stalemate. This often happens in beginner chess when one player is trying to checkmate their opponent with a Queen at the end of the game.
Draw by lack of material: If the game gets down to both of you having only a King each, then it's a draw. Nobody can win with just Kings. There's not enough "material" for anyone to win. But if either of you have even one pawn, then it's not yet drawn, because someone could still make a Queen from that pawn. So the pawns actually have to be missing from the board; it's not a draw even if the pawns are all blocked up. And if anyone has a Rook or Queen, it's not drawn. If you have only a few small pieces (Bishop, Knight) and no pawns, then it could be drawn. The rules are complex, and related to whether anyone could give checkmate. The most likely draws are Kings only, King+Bishop vs King, or King+Knight vs King.
Draw by adjudication: If a tournament has a formal adjudication process, the adjudicator can call a game a draw. If the game hasn't finished within the allotted time, it might be adjudicated as a win/loss, or as a draw. For example, if both players are down to just a King, that's a draw by "lack of material". Another example would be where there's no clear winner. For example, if both players have lots of pieces left, but it's all equal in terms of "material" (Queen is 9 Pawns, Rooks are 5, Bishops/Knights are 3, Pawns are 1). In such a position, the pieces and pawns are still equal, and an adjudicator would probably call it a draw. In fact, in positions that still have lots of play left in them, an adjudicator might well call it a draw even if one player has a pawn or two extra.
Draw offers; Draw by agreement. You can offer a draw to your opponent. If your opponent agrees to the draw, then the game is "drawn by agreement". You can say "Do you want a draw?" or "I offer a draw..." and if your opponent says "Yes", then you shake hands, and a draw has been agreed. But your opponent does not have to agree, they can say "No" or "Let's keep playing" or they can even say nothing at all in response (it's probably a bit impolite but legal). They don't have to agree, even if they are losing! And there is a complex etiquette in formal tournaments about how to properly offer a draw. For example, you cannot keep badgering your opponent with lots of offers of a draw. The proper way is a bit surprising, because you actually have to play a move! You are supposed to play a move on the board, then verbally offer a draw, and then press the clock. Your opponent can accept the draw, or can simply play a move back to reject the draw offer. Also, be careful, if you just offer your hand for a handshake, saying something vague, thinking you are offering a draw, you might actually be resigning. And once a draw has been agreed, that's final, even if one of you suddenly figures out a great way to win. You cannot agree to a draw and then ask the adjudicator to adjudicate it as a win later.
Draw by triple repetition: If the same position just keeps repeating, there is a type of draw called "triple repetition" or "threefold repetition". If the same position appears 3 times, then a draw can be claimed. In most cases, the repetition is due to infinite check with a Queen, but there are other cases too. In formal tournaments, the etiquette for claiming a draw by repetition is quite complex. In the official rules, a draw by triple repetition is not automatic, but must be claimed by a player.
Advanced Requirements for Triple Repetition Draws: And there are some quite tricky obscure wrinkles in what is meant by the "same position" appearing 3 times. The position must be (a) the same player's turn to move all 3 times, (b) the same castling right for all 3 moves, and (c) the same en passant right (very obscure).
Draw by perpetual check: If the position is such that one player is continually checking the enemy King, that's called a "perpetual check" or often just a "perpetual". But it's only really a claimable draw if there is triple repetition of exactly the same position. If one player is doing a dozen checks with the Queen and the enemy's King is walking all over the board, it's not actually a draw by a rule, although an adjudicator would probably adjudicate it as a draw. Players usually agree to a draw in these cases.
Draw by "No Progress": An adjudicator will sometimes award a draw based on their being "no progress". For example, there might be an effectively perpetual check with one player just checking the other. Or there might be a fortress type situation where there is no way to break through. Sometimes an assessment of "no progress" can be given even where one player is ahead on material. In beginner tournaments, no progress might occur because the junior doesn't know how to checkmate properly (e.g. Queen+King vs King, or Queen+Rook vs King checkmates). It may vary with tournament rules or with adjudicator discretion as to whether to award such positions as a win or a draw.
Draw by double time forfeit: In a game where a "chess clock" is used to time the game, if both players have run out of time, this is a double-time-forfeit, which is usually considered a draw. This often occurs where one player runs out of time, but the other player doesn't notice and keeps playing. (Note: the rules are somewhat complex if both players have run out of time on the clock, but one of them has checkmated on the board, for example.)
Draw by time forfeit with inadequate mating material. There's also an obscure draw in some tournaments, where if one player's clock has run out, they don't lose if their opponent doesn't have enough material to checkmate them. For example, if you have a Queen and King, against only a King, and you run out of time on the clock, it would be a draw because your opponent only has a King.
Draw by 50-move rule: There is an obscure draw rule that doesn't really happen in tournaments. The "50-move rule" declares a draw if there has been no progress for 50 moves. This means that there must have been no captures and no pawn moves. The only real purpose of this rule is to call a draw rather than allow players to continue indefinitely (e.g. in perpetual check situations or "no progress" type situations). For example, if both players have a King and Rook only, there won't be a win, and there likely won't be a draw by triple repetition. The player ahead on the clock could seek to win "on time" but can only really do so for 50 moves. In the official rules, a draw by the 50-move rule is not automatic, but must be claimed by a player. In practice, this rule doesn't occur in amateur level tournaments as players will agree a draw or an adjudicator will assess it as a draw.