Why were these moves considered mistakes/blunders?

isn't 16.Bd4 just lights out game over? also which moves in particular?

How so? I have Rf4, and then it's just a trade of queens.

Nearly every move in the opening. It calls more than 70% of my moves mistakes, inaccuracies, or blunders and I don't see why for any of them. I especially don't see how 9. c6 could be a blunder.

Oooooh! It wins me a freakin piece if I take the knight with the bishop. So it's a blunder as in "there was a much better move" not so much that it was a bad move.

9. 0-0 dumps a whole piece, if black plays accurately.

9... Bxc3 10. bxc3 Nxb5

15... Qxe5 is a blunder, white can reply with 16. Bxh7+ followed by 17. Bd4, winning the queen or mating.

17... d4 is also a terrible blunder, white's best reply is 18. Bxd4 and again black loses the queen or is mated.

21. Qh4 is bad because 20... Nf5, as played, wins the bishop (or worse if white forgets to move his queen)

Lots of other blunders, but they require more detailed analysis, I'll leave that for someone who has more time than me.

Yes, 9... c6 is a blunder because you failed to capitalise on white's blunder. You can win a piece.

"15... Qxe5 is a blunder, white can reply with 16. Bxh7+ followed by 17. Bd4, winning the queen or mating."

In case you wonder why not just immediately play 16. Bd4, black has 16... h5 and is better.

16. Bxh7+ removes this resource and wins the queen for two bishops.

"17... d4 is also a terrible blunder, white's best reply is 18. Bxd4 and again black loses the queen or is mated."

I'm a little inaccurate here. Black doesn't lose the queen, he again has 18... h5, but he still loses the bishop after 19. Bxe5 hxg4 20. Bxc7

Don't I still have Rf4 here and it's a trade of queens at worst? I don't see how sacking his light square bishop makes Bd4 any more feasible.

Read post #9, I clarify why 16. Bxh7+ wins the queen.

And Rh4 doesn't work since white can play Qh3+, dodging your rook with check, before grabbing the queen. Of course, this assumes white also played Bxh7+. If black declines to capture the bishop with 16... Kh8, 17. Qh3 is even worse for black than simply giving up the queen for two bishops.

Without 16. Bxf7+, white isn't nearly as good. It's a fine sacrifice that exposes your king and removes the pawn, stopping you counter-attacking his queen. If white doesn't play Bxf7+ and immediately plays Bd4, then yes, Rf4 is a good defence, as is h5.

Aaaaah I see what you're saying. Yeah that would be bad for me lol. I did look at his bishop and consider sacrifices (as I'm sure he did). But I didn't consider he could use that sacrifice to get out of trouble later.

I misread this post for some reason, I've deleted my reply and will try again. 16. Bd4 doesn't work, black has both 16... h5 and 16... Rf4 (as kthprog points out) to save the position.

16. Bxf7+ first, that's lights out game over.

White drops Pawns with moves 8 and 13 and missed a game-winning move 16 Bd4.

Lots of blunders on each side.

I suggest you download your games as pgn files, then load them into freeware like (for Windows) Lucas Chess, where very detailed analysis including many alternate moves can be seen for each move.

Black can dodge the bishop sac with 16... Kf7, but this isn't good either. 17. Bd4 still causes problems, and now your king blocks the rook from saving. Granted, you save the queen and don't get checkmated, but it's still horrible.

16. Bd4 isn't winning, we've been discussing this. 

16. Bxf7+ first, otherwise black has h5 or Rf4 to save the position.

the first few moves feel akward, the knight doesnt belong on c6, because you really want to play c5 first with your pawns on e6 and d5 and only then Nc6, your light square bishop is hemmed in and i dont see a future for it. And because you cannot play c5 it is quite difficult to get your rook going on a8, with c5 in the position it can quite nicely develop to c8

@kthprog As thumb rule, if you aren't sure why just check the analysis itself! It gives you the better move, and indeed, chess improvements consist of finding a stronger winning move or not losing so that accounts for both (ie 9.0-0? Bxc3 -+ and 15....Qxe5? +- (also thumb rule, the exposed queen on e5 in the French structures is rarely good)).

As for the opening, anti-positional moves are played; I've played the French for quite a while and the structure turns out non-French early on.

In the language of computer analysis, the terms "mistake" and "blunder" generally mean that the evaluation of your move differs from the evaluation of the "best" move by a certain amount (more for a blunder, of course). So your moves were labeled as mistakes and blunders because there were better, or much better, moves available.

One simple example: 9...c6 was a blunder because you had 9...Bxc3, winning a piece by removing the guard on the Bb5