Assuming you got a basic VST drum machine included with Cubase, you'll need to either program your own beats or find some midi files with drum beats on them. You can also buy loop collections that have midi files included.

If Cubase didn't come with a drum machine like the LM-9 or LM-4, you'll need to buy one. (like Battery for instance)
In order to program it you'll need to either input the notes manually in MIDI or use a MIDI or USB keyboard.