there's a few books you could check out like Scott Cunningham's book Oils Incense and Brews.
a potion is basically any liquid spell, be it oil, lotion, tea, bath...
keep in mind not all potions are meant to be consumed, some are suppose to be worn or buried or hidden around your house. be sure you contact a doctor to see if it's wise to ingest certain things, say if you're allergic, taking medication, or pregnant for example it could be dangerous to you. if you know you're fine, i'd then research the herbs you're using to be safe.
there's some forums and articles on here to help, and i know of a few people who also study potioncraft, that's just a few key points. hope it helped ^_^