how do people form/find relationships?

I'm 19 & i've never been in a relationship, or even close to being in one. I've never understood how people just find people to be in relationships with lol, maybe it's because i'm ugly but i really don't understand the concept. I can barely find people who would want to be friends with me, I can't even grasp the concept of someone even wanting to be in a relationship with me lol ??.