In chess, there are a ton of rules that you will need to keep in mind when playing chess.
The major rules that you need to keep in mind about chess are these as listed: Checkmate, En Passant, Castling, Pawn Structure, Stalemate, Piece Activity, Attacking, and 50-move rule:
Checkmate is simply when you trap the king while the king is in check and has no safe squares to go and that includes the square that he is currently being attacked on. The most important step with the king is to keep the king safe by simply playing safe moves to prevent the king from being attacked.
En Passant is a French pawn capture technique that is only possible when your opponents pawns is next your pawn and it is only possible when you move two spaces in your first move with your pawn. Fail to do so violates the rule to capture En passant.
Castling is an awesome strategy to keep your king safe. This is only possible if you haven't moved your king and/or your rooks. If you do move your king and/or rook, then you can not do this technique. It is best to castle early to develop and perform the defense of the king. There are two types of castling: 1. Kingside castling (0-0); 2, Queenside castling (0-0-0). Either way that you want to castle is fine unless if you know what to do in every chess game and in every situtation. Do it safely and tactically.
Pawn Structure results the skeleton and is a good indication toward where your pieces go. Knowing that pawns move forward and not backward, pawns can only capture diagonally.
Piece Activity is an important rule to understand the movements and what is going on on the board after making a move with a piece in the game. It is significant to learn chess notation to better understand the names of each of the squares of the entire board.
Stalemate (1/2) is when the game ends in a draw because the king either has no available spaces to move, the king is in a safe square but has no safe squares to go after the king makes it's move and it is the only piece that you can move; these are all examples of stalemate situations.
50-move rule is a rule that involves when players don't make any moves and capture within 50 moves, the game is considered to be a draw. It is significant to keep playing the game with the pawns to keep the game going.