Check levantar and levantarse in the dictionary. Your sentence doesn't say what you have to raise. Duo's reflexive construction indicates that it is yourself that you have to "raise."
Spanishdict.com will also give you the conjugation of levantarse, in case reflexive verbs are new for you. (Verbs used when the subject of the sentence does something for himself: brush your teeth, comb your hair, wash your hands, etc.)
Another help: studyspanish.com (Grammar Unit Five). Explanations, examples, free quizzes!