There are 12 sliders for drums selection each with all the available 48 QT drums.
You can adjust the volume of any of the 12 drums with the volume sliders from OFF to the full MIDI velocity of 128.
You can hear any drum selection by mouse-clicking the large buttons with drum numbers, or when you click within a BOX to place where a drum is to sound, or by hitting the number keys 1 - 0 for drums 1-10 with the - and = keys for drums 11 and 12.
With this setup you can "play" the app like a drum machine if you like.
At the bottom left of the window is a popup for the selection of drum kits; try them all, SFX and Orchestra can yield some interesting sounds.
To play an example, mouse-click the PLAY button or tap the Spacebar. The PLAY button will change to a STOP button; click the button or tap the Spacebar to stop PLAY; the button name will change to PLAY.
You may Pause the example if you like, tap the P key and the example will stop on the present beat; tapping the P key or the space bar will cause the example to resume PLAY from that point.
Note that the way the play loop is set up, you can change parameters while the example is playing; there will be a slight pause with menu selections; it should be nearly immediate with key presses.