I think it depends. If you want to say "Mark is like John" it would be "Mark est comme John". Est being the relevant part of Etre. If you were asking a question, for example "you mean like John" it would be be something like "vous voulez dire comme John" (you mean to say like John) or "tu veux dire comme John" if it's someone you know well.
I could be wrong though, I'm no teacher. If you need short translations for things that aren't complex, Google translate is not flawless but pretty good: Google.com/translate