"I want to meet them later."
Translation:Jeg vil møte dem senere.
It depends on the context. The verb "å treffe" is maybe more a short meeting where you just say hi, while "å møte" might imply that you're talked a little bit longer. You will definitely be understood if you mix them, so you should not worry about that!
"Møte" as a noun is just like the word "meeting" in english. "Jeg har et møte med kollegaene mine" = "I have a meeting with my colleagues".
(Another fact about "å treffe" that might confuse you even more: "Å treffe" could in another context also mean "to hit" as in "Jeg treffer målet" = "I am hitting the target".)