I saw that swimm5001 made these for his "Get the Look: Crisp & Clean", I've made three different layers and they have the same colors but different shapes.

The problem is when I try to "combine" them, they aren't transparent, when I put a layer on top of another, the layer under can't be seen. How do I make them transparent?

Hope someone can understand what I mean

btw I tried searching but couldn't find anything that was of help. I use PS6

TIA