Reisen is a genereal term for travelling. Ich reise gerne. I like travelling. Verreisen means travelling as well, however with a focus on going away from home/not being at home. Ich verreise gerne. I like travelling (because I like to be away from home, because I appreciat different surroundings than the usual). Im Sommer reist er immer. He always travels in summer. Im Sommer verreist er immer. He's never at home in summer.

Reisen is more like travel to a place you already know, and verreisen is more like you just wanna scape from home. I hope it can help you.