Why move my knight here???

I had the following game where I was playing as black:

You need to finish development first, and that knight move also helps you to control important central squares.  The computer also prefers moving either of your bishops to the pawn move.  Yeah you have to keep an eye on the white knight, but your job as black out of the opening is to equalize first through development.  Get your pieces on their best squares first before advancing your pawns.  Or so I've read...

Personally, I would have chased the white knight away with a pawn to a6 first, then decide what to do next. But as a general rule, the phrase "a knight on the rim is dim" is fairly accurate, especially in the early stages of a game. Even in the in the middle game, most higher level players don't want to put the knight on a edge of the board.

That being said, it's not uncommon to put a knight on the edge of the board if your just repositioning the knight and know for certain it won't be on the edge very long.

But in general, it's a bad idea to put a  knight on the edge of the board and forget about it, unless your opponent forces it to the edge, or it's close to the king and playing a defensive role.. and even that should be an uncommon if not rare occurrence.

Time for me to sound like a broken record: You need to read the book Logical Chess: Move by Move by Irving Chernev. Not only will it help you understand why you should be developing your pieces towards the center this early in the game, but it'll also answer your questions about when and why to move your non-center pawns.

Hey everyone thanks for the feedback- this definitely makes sense.

Appreciate the advice and the book recommendation - I am going to buy that now.

First of all, although 10...Nc6 is better than 10...a6, you choice is by no means a bad move. I wouldn't worry t much about making the second best move in most positions. In fact, if you always made the second best move, your rating would skyrocket! 

So, what are the differences in the position after 10...a6 11.Nc3 Nc6 and the position after 10...Nc6? It seems to me that White's knight is better on c3 than b5. But 10...a6 isn't a bad move. The key to chess improvement is in avoiding the big mistakes, so that's where you should concentrate

imo, the knight is not in a good place, so leave it where it is, if you finish developing and put pressure on the center, they will need to spend a move repositioning it anyways

Agree, in concrete terms the Nb5 is misplaced because whilst it looks dangerous at first glance it is not actually threatening anything. Only thing to watch out for is Bg5 and Bxf6 by white when you have to recapture gxf6 to avoid losing the d6 pawn. But this is ok for black and you can even castle queenside. a6 is not a terrible move, but it rather chases the knight back to where it will need to go anyway at some point. Continuing development and increasing central control with Nc6 is better. 

A6 looks good but there is no hurry to force the retreat. The knight is not doing much and allowing it to do nothing gives you time. 

 I read to not move a,b,c pawns until the motive of White's Q is clear and to move a,b,c pawns in an effort to deter this motive, of white's queen.