How Are Some People Just So Naturally Outgoing?

I try SO hard, not to be so shy. I just don’t understand how people can just start talking about things to anyone. I can’t do it. I try to make myself not worry about others, and say whatever comes to my mind when I’m around them, I want to talk to people! But when I’m with people besides my friends absoluelty nothing comes to my mind to say. I feel like I’ve tried everything, I’ve even tried not trying and that just makes things worse. How do you just talk to random people? Like say at the register. Please help, I’m willing to take any advice!