Click on the rectangles to create a beat. Click on the 'click for more tracks' to find more drums. Click on the example buttons to load in a pre-made beat. Click on the loop on/off button to turn the loops on and off, and the circle to select a loop. Click on the up/down arrows to change tempo. Click on the 'random' button to create a random beat.
More drums and loops coming soon, or maybe never. (2024 update: probably never!) NOTE: Some loops will be designed for a tempo of 60 so they may not work well for other tempos.