What should I play here?

these games aren't currently ongoing are they? if so, you can't ask for advice here

all of them are finished games

In the first one I would play Nxc5.  If you play b6 you just weaken yourself.  Even if you follow up with c5.  You will always be stuck with something for white to bite at.  At least my way white has to use his b pawn and wait a few moves before he has created a weakness on your side.

In the second one I would take with the d pawn.  If you take with the c pawn you let white poder about a minority attack.  Taking with the d pawn keeps thing symmetrical and dull though.

In the third one I think white played b3 because if you don't take, he will take on c4 and you will be fixed with weak pawns and he will have easy play with, in my opinion, a little more than compensation.  If you take on b3, he will recapture with the pawn and then his rook on a1 becomes active and you will have a painful time baby sitting your a pawn.  in that position he has an excellent bishop and rook though b4 is black's.  But with good compensation.  I would have played the same move 11. b3 if I was white.

1st position: ...Nxc5 is not a positional concession. If it was, ...b6 might merit consideration. As it is, ...b6 creates a weakness on c6 for no good reason

2nd position: ...cxd5 allows Qa4+ followed by Ne5 when White has all sorts of ideas for how to attack depending on how Black responds. It could be g4 followed by h4, or Bb5, or Nb5 followed by Rc1. ...exd5 or ...Nxd5 are much safer moves.

3rd position: b3 allows White to find a way to make use of his currently useless pieces on the queenside. I mean, what else is White supposed to do with the knight, dark-squared bishop and rooks? Black needs to play ...cxb3 in order to keep the pawn, but then all of White's pieces make sense: Bb2, Nbd2, Rfc1. Black's queenside probably will not hold in the long run.

I think b6 and Nc5 are both equally good. 1.b6 if you are playing for a win, since after Nb3 you can play c5 immediately, since after dxc5 bxc5 Rad1 Rac8 the d7 knight will be coming to e5-d3. If white doesn't play dxc5 then you can play c4 and b5, and create a passed pawn on the queenside.

@Bab3, are there any better moves for white which take advantage of the hanging pawns?

Not sure about b3, doesn't seem like a good move.

exd5 is definitely better, agree with Bab3 on this.

Please tell me if my lines don't make sense,  I havent used an engine.

Of course I firstly check with an engine, but this is not a good way to improve.