Something that's dreamlike feels like a dream, or seems unreal. The empty city streets just after a snowstorm can seem dreamlike.
A dreamlike story is odd and a little surreal — for example, the story of "Alice's Adventures in Wonderland" is dreamlike, with talking animals and playing cards and drinks that make Alice become larger and smaller. Being at your school on the weekend, when no one else is there, is dreamlike, and winning the lottery would probably feel a little dreamlike too.