When to send a message?

New to OKC, and I was wondering, when do you generally send a message to someone? Do you visit their profile, "click like", and then wait to see if they end up liking you back before they message you?

I've only ever used Tinder before, so I'm used to their system and I'm just wondering how it's supposed to, or how you feel it's supposed to, work on OKC?

Thanks for any help!