This is being used as the imperative form of the verb. You conjugate it based on the verb stem (remove the -en or -n, depending on what the dictionary form is).
Basic explanation: For imperative du, you use the verb stem. For imperative ihr (plural you), you use the verb stem + T For imperative Sie, you use the dictionary form and add "Sie" after the verb.
Example: schlafen (You) sleep! = Schaf! (Plural you) sleep! = Schalft! (Formal you) sleep! = Schlafen Sie
For more details see http://www.dartmouth.edu/~german/Grammatik/Imperative/Imperativ.html