"My books are under the desk."
Translation:Mis libros están debajo del escritorio.
Because, I am told, under is debajo de. The de then combines with the el to form del. Try thinking of it as underneath, debajo de then feels a bit more natural.
Abajo - below, debajo de - under. I believe that the Spanish then use them the same way we do.
I said "bajo del buro" and was marked wrong, it was supposed to be "bajo el buro". But here I see "debajo del escritorio" as a correct answer. Now I'm really confused...
Baja del buró, (note the d in del & the accent in buró), means under the bureau/dresser/chest of drawers. Desk is escritorio.