"Do you enjoy surfing the internet?"
Translation:Ĉu vi ĝuas retumi?
The root is "reto" which literally means web, net, or network.
"-um-" is an infix that doesn't have a set meaning. With nouns, it's like adding the word "thingy". With verbs, it is like verbing a noun. "Retumi" could probably be translated as "internetting".
So, super-literally perhaps, this sentence would translate back into English as "Whether you enjoy to network-thinging?" What threw me off about translating this from English into Esperanto is that I was expecting to have a noun after retumi.