"Schlaf nicht ein."
For those who don't understand this tricky one: it's normal if you were not able to translate it because this phrase shouldn't be at this level. Actually, the program considers that you know the words "schlaf", "nicht" and "ein". But it is in fact a new word since it is the verb "einschlafen", which means "to fall asleep". Plus, it is an imperative form that we haven't learnt so far, hence the complication with "Schlaf ein". However, "nicht" is a word that you should be familiar with:)
It's part of the verb "einschlafen". http://german.about.com/library/anfang/blanfang19.htm