Pin the Kingside Knight and Double Up
Pinning the King’s Knight with a Bishop is a very common pin. For White, this means playing Bg5 against Nf6, where it is pinned against the Queen on d8. The goal is to “double up” on the Knight, by White also playing Nd5. It doesn’t usually win the Knight, but you can often ruin the Black kingside pawns in this way. This can be saved by protecting the Knight by Be7 or Nbd7, or sometimes by escaping the pin with a Queen check (e.g. Qa5+).
Diagram: Bg4 Pins the Kingside Knight
Diagram: Black Doubling Up on the Pinned Kingside Knight
It also works in reverse for Black, of course. The White Nf3 can be pinned by Bg4 followed by Nd4. If possible then Be2 or Nbd2 is a savior. And the Queen can escape by Qa4+ or Qb3+ or some other check.