Why are these moves recommended?

Question

I am playing chess on the chess.com app with the top three suggested moves:

I am an amateur. I get the basic idea that developing your knights is a common, good thing early in the game, but why is that specific pawn move a7-a6 recommended? The queen could take it, but it’s protected by the rook.

Answer 1

The point is that 4...Nc6 could be met with 5.Bb5, when the knight is pinned and it's likely White will exchange it off with Bxc6. Without the c6-knight, Black will lose some influence over the key d4- and e5-squares. Playing ...a6 before developing the knight aims to prevent this.

Of course there's a trade-off here, since Black is spending a tempo just to prevent a relatively innocuous exchange.

Answer 2

Things you should consider this early in the game before playing your next move:

1. Development of your pieces
2. Control Over center
   

If you do not know about these, try reading about it before you play your next game. You'll see improvement on your own.

If I were to show you a blunder-filled game from black (see below). You can clearly see few moves wrong from here and black is down on pieces as well as defense is broken. White is easily winning. But this is highly unrealistic TBH.

[Event "?"]
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1. e4 e5 2. Nf3 d6 3. d4 exd4 4. Qxd4 Be7 5. Qa4 Nc6 6. Bb5 a6 7. Bxc6 bxc6 8. Qxc6 Qd7 9. Qxa8 (4. Qxd4 Na6 5. Bg5 Be7 6. Bxe7 Qxe7 7. Qxg7 )

But those recommended moves remove a lot of pressure of black and keep the balance of the game equal.
1. Evaluating a6:

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1. e4 e5 2. Nf3 d6 3. d4 exd4 4. Qxd4 a6 5. Qa4 Bd7 (5. Bb5+ axb5) (5. Nc3)

You can see clearly Bb5 is not at all good for white now. 4. Qxd4 a6 5. Qa4 b5 make white underdeveloped as white has to save the queen from the pawn. Even after using Nc3, Na4 or Na5 are just loss of tempo for white i.e, bad moves. Although, white can recover from here but so can black improve himself here.

2. Evaluating Nc6

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1. e4 e5 2. Nf3 d6 3. d4 exd4 4. Qxd4 Nc6

You can see here the queen is under attack and the knight at c6 is covering 4 different squares a5,b4, d4,e5 and also e7 is possible if needed. And this also stops direct check threats to the king (Honorable mentions here would be that black has now one free space to move the rook and he is one step closer to queen side castling).

3. Evaluating Nf6 :

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1. e4 e5 2. Nf3 d6 3. d4 exd4 4. Qxd4 Nf6

Similar to Nc3 discussed previously, Nf6 strengthens control over center by putting pressure on pawn at e4, d5 and controls g4 and h5 for now. After Be7 black will be able to do king side castle. This also saves queen from being harassed by Bg5.

All in all these are actually the better moves you should play here. Because if you don't white can easily take a lead and even if you are able to save your pieces, white will easily be able to mess up your pawn structure. Thank you for reading.

Answer 3

They suggested you play a6 to prevent the white-squared bishop from playing to b5...which will be a bad start to the game.