Yes, you have to do it in steps. A real TB303 is very similar apart from the way you play the finished patterns back (and the superior sound!!) and it doesn’t have a helpful LCD readout to show which event you are editing

This is all off the top of my head so apologies if some bits are incorrect.

Flick it in to pattern mode and clear the pattern that is there with the pattern clear button. If you push play at this point then you should have no sound playing.

Click on a note on the keyboard to illuminate the note above it. That note will then play as rebirth/303 runs through the 16 events in the bar. Now, to edit the next note you need to click the “step” button. Place a note somewhere on the 2nd event to get another tone and so on and so forth. Use the “step” and “back” keys to travel backwards and forwards through your pattern to edit notes. Obviously you don’t need a tone on every event if you don’t want to so you just leave it blank.

Once you have got a basic pattern going, play with the other buttons on different notes to see what they do. eg, you can add an accent to each note and transpose it up or down. You can join notes together “slide” etc etc….

Once you have mastered that pick your waveform, add a bit of distortion and twiddle the squelchy knobs till your heart is content.

(if you want to make a long 303 pattern you will need to flick to track/song mode and copy your patterns across to your desired position using the “loop” markers to place it. Then whack the loop from 1 – x [x being however long your track goes up to] then hit record and twiddle thy knobs! It will then be recorded and automated)

Hope that’s as clear as it can be on a Friday night.