How do you just "hook up"?

This is probably going to sound weird , but I've never really understood how people just hook up for a night? I was with one guy for five years, we recently split, and he was the first and only guy I've ever had sex with. I guess I'm sort of narrow minded because I can only see myself being comfortable having sex with someone I love and have a true emotional connection with . Being 22, I see hookups possibly happening somewhere along the line, in my future before I jump into another serious relationship. Someone once told me that you dont really think about hooking up, the feeling just overcomes you and you give in, is that true? I'm always worried I'll feel bad about myself afterwards if I do ever hookup with someone. What are your opinions ladies?