? This is a horrible move, it blocks the bishop and the only space that the knight can move to. If it is so you can castle, your choice to castle on the queenside is questionable. The position looks weak...
6... Bf8e7
Development at last... a bishop is brought to the fight...
7. O-O-O
Castling is generally a good idea, it should move the king to a safe square and develop the rook, however the lack of pawn development in the centre means that this rook although on it's most powerful square is pretty useless
7... a6
Good defensive move, denying access to the knight on C3 to B5. Also the pre-cursor to Pawn-B5. Now black knows where to point his attack because white has castled
8. f3
White attempts to regain some space by attacking blacks forward G Pawn. If black takes white can retake with the knight and develop another peice
8... d5
Black ignores the pawn exchange on F3 and gambles on D5... Black hopes to clear the 2 knights and 2 pawns from the board whilst bringing his queen to a powerful central position with... E4xD5, NxD5, NxD5, QxD5
9. Qe2e1
White loses another tempo here, basically allowing black another free attack
9... h5
Black backs up his previous decline of the F3 pawn exchange and supports the advanced G pawn further limiting whites kingside development
10. Bf1d3
?? Although you are developing a peice you have moved it to a prone position, it can be attacked with ease by the pawn push to C4 or by D5xE4
10... c4
!! I love this kind of tactic, you are attacking a peice with the pawn you just moved but looking deeper you have revealed an attack against another peice. It is possible for players to miss these second attacks, so employing them against high value material is a great way to win games... This move actually won this game I believe.
