Uh, one causes the target to be sleepy, the other confuses them (similar to the neurological poison of poisoner thieves, I guess), and the last one just straight-forward poisons them? At least that's what I get from the words sleepy, confusion, and acidic. I couldn't tell you if it's worth practicing them or not but if you're new to assassin you should practice all the skills so you can get first-hand experience on how they work.