For TouchMe, we recommend starting with the Dot Piano, just to experiment. Especially for Playtron, we created a Playtronica Sampler with over 20 free sound packs!  Then move to other synths, and try tweaking parameters (randomly) and see what happens. This is the best way to learn about synths!  See more on our tutorials, including how to start with TouchMe and how to start with Playtron quickly.