In order to create a looped playback, right click on the 'play' button and select 'loop'. Open the transport window and select 'loop playback'. First, select a track, expand 2, and select session drums (you can take any other track) for the patch and also create a 'click track' which will be available in the track menu. A stereo instrument track with expand 2 is used here. This video shows a quick and easy way to create a drum loop using 'MIDI MERGE'.
