In Generations, you are able to create potions using the Chemistry Set. You can work on your logic before trying to discover potions, or you can simply learn Logic when using the Chemistry Set.
Here is a list of all the different potions, the levels you can create them at and their uses.
With most potions, comes a special moodlet. With exception to the Ninja Vanish & Young Again, here are the other 8 moodlets. Ninja Vanish does not have a moodlet (I believe) & the young again just gives you the regular “Having a blast” moodlet.
The Young Again Potion does bring you back from Elder stages to Adulthood, but Young adult is as far back as you can go. You can only use this potion as an young adult or older. Teens cannot use this potion.
The Ghost potion, temporarily turns you into a ghost, and during this time, you can woohoo and have a chance of conceiving a ghost baby.