"I am behind you."
Translation:Ik ben achter je.
I didn't try it because I hovered over "you" before I answered, but should "jou" be accepted in the place of "je"?
You conjugate the verb to match the subject. Check out the information available if you scroll down a bit on the Basics 2 lesson webpage for some more information, but basically it goes like this:
Note that in cases where "jij bent" is inverted, the -t is removed from bent:
"Jij bent gelukkig. Ben jij gelukkig?" ("You are happy. Are you happy?")