This is the 15064th most frequent German word.
sollst
"Shall" or "should" (second person singular of "sollen").
Here, 'sollst' is used to express an obligation or a recommendation.
Du sollst dein Zimmer aufräumen.
You should clean up your room.
In this sentence, 'sollst' is used to inquire about a reason for an obligation.
Warum sollst du immer die Hausaufgaben zuerst machen?
Why should you always do the homework first?
Here, 'sollst' conveys advice or a recommended action.