Chess notation is simply a form of shorthand for writing down the moves of a chess game. In order to improve in chess, it is important to be able to review games. This is a great way of accessing previously played games. In addition, completed notation is required to enforce many chess rules. Algebraic notation is standard in the US.
There are many online resources available for learning notation. ALL players are highly encouraged to take notation, and it is a requirement in most in person tournament sections when the time control is G/30 or longer. Bring two sharpened pencils and a notation book if possible.
Online events do not require hand written notation, as the system records the moves for you. For online tournaments on ChessKid.com players can access their game history to analyze their previous games at www.chesskid.com/me/game-history.