A checkmate is the goal of Chess. This is when you attack your opponents king without them having the ability to move to safety. Take this position right here: black is checked by the pawn but the king cannot move to safety so this is checkmate.
Here are a few easy Checkmates you can use on your friends who don't know how to play chess:
The Fools Mate:
This is the fastest checkmate black can achieve, it's in two moves: it starts with white playing G4 then black plays E5, white blunders and plays F3 "protecting the other pawn" then black ends the game with queen to H4 checkmate.
Fools Mate for White:
The Fools mate also works for White except it takes three moves to checkmate. It starts with white playing E4, then black responds with G5, white plays D4, and black blunders with F6 then white plays queen H5 checkmate.
Scholars Mate:
This is most likely the first checkmate beginners to learn on lessons but Imma show y'all again. It starts with white playing E4 then black responds with E5, white plays bishop C4, black plays knight C6, white plays queen H5 attacking the pawn on e5 and the pawn on f7. Black attacks the queen by playing knight f6 thinking it's a good idea, but white stuns black with a stunning queen xf7# checkmate.
So yeah. use these Checkmates to win against your friends are just people who don't play chess in general. Keep in mind if you try to use these against bots like Martin or against people who actually know how to play chess they might not work. If you want to learn how to counter these mates, check them outton the Chess.com lessons.