How do you comfort someone?

I'm actually someone who doesn't want to care with other people's affairs or problems but because of my conscience, I always end up having to comfort other people. Sometimes it's not even intentional, they just come at me for advice and even cry infront of me. I'm gonna be insensitive about this but on moments like that, I just want to leave and sleep or something. But it's not like I can just do that when someone is hurting. But the thing is, I don't really know what to do. I should listen to them if they have something they wanted to share but what should be my responds be if they full on message me on messenger? If it was in person, I'd hug them to comfort but if it were virtually, how?