Whats the deal with a minority attack? With less material on a given side of the board, you would think the attack would fail.

A minority attack aims to undermine the opponents pawn structure and create weaknesses that may be taken advantage of. 

It is not an attack as in going for the king but rather more of a positional thing (i think).

Eg in the Queens gambit.

this b4 push is to try to exchange at c6 to try to weaken the pawn at c6. or expoit any holes that may occur at c5

The minority attack is a positional theme.  The idea is to create a weakness that will then be exploited by other means.  Although it shows up in many openings it is most prominent in the exchange version of the Queens Gambit Declined (ECO=D35?). If you check some older books you can find some good games on it.  I remember, but cannot find right now, a book by GM Evans with a good example and explanation.

So you think 13...b5 would be the response and then wheel the N to to a4 then c5? What about if Blk goes a6 to prevent the advance?