All which follows assumes you want your drums on one Syntakt track.
You can enter Grid Record mode by tapping [REC]. In this mode, tapping a trig toggles it on or off: holding a trig and fiddling with controls lets you “parameter lock” the trig. Syntakt tracks are mono, in two senses: they can only have one trig per step, and when you use a Machine you can only trig one note at a time (multiple oscillators notwithstanding). When you add trigs to a MIDI track, that trig can be set to send four MIDI notes. You can’t “pick up a note and move it on top of another note” like in Ableton; you’ll have to hold the trig and set it to play two notes at once, either by tapping a note on an external controller, or by picking the notes you want using the knobs, on the SYN page, I think.