So often in my games, I find myself placing pawns on the same-coloured squares as one (or both) of my bishops, sometimes trapping them inside. Are there any situations where it is useful to have your pawns and bishop(s) on the same coloured squares? Dumbed down please, I'm only a beginner.

In situations where you only have one bishop left the general rule of thumb, usually atributed to Capablanca, is to place your pawn on the opposite colour to that bishop. This way the pawns won't obstruct the bishop while helping to control the squares unavailable to it.

Of course there are always exceptions to this rule but they probably don't matter too much for you right now.

It's almost universally useful to put the pawns on the opposite color of their friendly bishop or to move your bishops to the outside of pawns locked on their color.

The one exception I can think of is in opposite color bishop endings the weaker side can sometimes find an easy fortress by placing all this pawns on the same color as the bishop... although this abandons half your squares and hinders the bishop's movement (as usual) you effectively make your pieces immune to the only piece your opponent has left.  Basically a permanent blockade.