Well, the same as in desktop DAWs, lol.
Actually, wouldn't call exactly Caustic a DAW. Isn't created around manipulating audio files (at best you can use audio files as samples in PCMsynth), it's more of a sequencer with lots of synths. It's actually a simpler, more designed for small screens version of Reason (but then again, never tried Reason myself).
At least it has actual synths, though. Cubasis and FL Mobile are both sample-based, so both have only premade sounds IIRC.