Are Gravitational Waves Creating Black Hole?

Is gravitational waves like black holes crashing into each other? They're part of the reason the universe is expanding, or does it contract in some places and expands in other places? Right? Like when the gravitational waves get generated, does it compress space? That's a really interesting question. I'm not 100% sure of the answer, but I think that this is only a positive contribution to the shape of space.