How do you start relationships?

I realized I was poly around 2 years ago. For most of the time since then, I was with a partner that wanted to be poly, but just wasn't. Since breaking up, I've had a few hookups with a coworker, but didn't feel like continuing with them.

I currently have crushes on at least 4 different people, but I don't know how to do anything about them. I doubt most of them are open to polyamory, and I'm scared of seeming like a creep. What situations is it even ok to ask someone out?