Read something about Bishops that I didn't understand

It said that if there is a bishop and pawns left on the board, then you should keep your pawns on the same color square as your opponents Bishop. It didn't really explain why. This seems to go against my thinking as I thought you would wanna keep your pawns away from squares a Bishop can attack. 

What was the context for the statement? Was the person commenting on a particular position? As a generality the statement is false.

It depends on the position.  Keeping them on the same color can be a very good way to restrict the enemy bishop.  If you already have a nice space advantage, then this strategy can even be completely winning for you.

A few big considerations in endgames are

1) activity of your pieces

2) the targets (usually weak pawns)

3) ability to create a passed pawn

So if the pawns are on the same color as enemy bishop, but the bishop can't get to the base of the pawn chain (the undefended pawns) then there's nothing to worry about.  The big consideration then becomes how active your pieces are.  If your bishop is also that color, then you've really restricted your own bishop (usually you want pawns on the opposite color of your own bishop)... but if you can target his weak pawns, then that doesn't matter much either.

In positions where it really does make your pawns weak (the bishop can attack them), or gives your opponent a pawn break to create a passed pawn (the bishop will support pawn breaks on that color), then putting them on the same color would likely be a mistake.

If the biggest consideration is you have e.g. connected passed pawns, then you likely wouldn't want them on the opposite color because they may easily be blockaded.

It is Capablancas rule in Bisop/Pawn endings. 

With Bishop of opposite colors, keep your pawns on the same color squares as your opponents Bishop. 

With Bishops of the same color, keep pawns on the opposite color squares.

Is that how he says it?  Much simpler to say it in one go... keep pawns off the same color as your bishop.

                Think counter attack.  If your pawns are on the same color of his bishops, you want a pawn chain. He can take, but then he'll lose a bishop for a pawn.   pawn chain

This keeps the opponents bishop from moving across the board(freely).  No one wants to exchange a bishop for a pawn.

Can you show the position? There are many questions: Where there opposite colored bishops? is one, for instance

Mind Scramble alert.