Press START. Pick a beat and a machine from the menus. Click the labels under the keys to choose which drum you are editing, then click the sixteen keys to change the pattern.
The TR-808 and TR-909 each show their own photographed panel; pick one and the window changes. Drag any knob with a red arc. Knobs without one are dead on purpose — TONE and SNAPPY shaped analogue circuits a recording has already baked in.
It has no kick, no snare and no hi-hat — it is pure Latin percussion. Load it and the beat still plays: every part falls back to the nearest drum that machine actually has.
The machine menu lists all 443 machines in the library. The four at the top play; the rest are greyed out because their samples are not in this page. The full app plays every one, and exports your loop as WAV or MIDI, which a web page cannot do.