Annotated chess game

Don't give away anything for nothing. The pawn is undefended. Did you overlook the move lost a pawn, or did you hope that your opponent would not see Qxg5? Don't play a bad move and hope your opponent will play a worse move.

You should start developing your pieces with ...Bg7 or ...Bb7.

The knight cannot defend itself so it doesn't count as a defender. The minimum amount of defenders you need so a piece is safe is equal to the number of attackers. Here your knight is defended once, by your king, and attacked once, by his queen. It is good to play 14...Bg7 to overprotect the f6-knight so you can move your king away without losing a piece.

Your knight on f6 is defended once and attacked twice. The only moves were 15...Bg7, 15...Rh6, or 15...e5. Edit: no, it generally is good to win tempi or force the opponent to give up the bishop pair (which is worth half a pawn). However, you can add "unless there is a tactic" to all guidelines, and here this is a blunder because both your knights are not safe. White's last move was 15.Bc3, you have to think, "What does this move threaten?" Here, it threatens the f6-knight, so you need to count attackers and defenders to see if your opponent's last move threatens to forcibly win material. Your knight was defended once and attacked twice, so you needed to defend it one more time to make it safe.

Your knight on f6 is still en prise. Even worse, after 17.Bxf6+ Ke8 18.Bxd8 costs you your queen.

You resigned too early: you still have several pieces left and a chance if your opponent made a mistake. Your play is improving, make sure your moves don't leave your pieces en prise or forcibly lose material. Check out this article www.chesscafe.com Miscounting is something that we all do, keep up the improvement.