The Importance of the Kingside
Alot of beginner players make the grave mistake of weakening their kingside in the opening, this is a big mistake as it would just give the opponent lines to attack your king, as can be illustrated by this game,
So that game just went to show how devastating an uncastled kingside attack can be, so beginners beware! Never play f6 in that line and only push out your pawns on the kingside in the opening if you are absolutely sure they will not become a weakness or if they would benefit you! Also, keep an eye out for any kingside weaknesses your opponent crops up and exploit them mercilessly like white did in the game!