like Lonicera said, research the herbs before using them, and speak with your doctor for an allergy test to see if you're allergic to something.
a potion is any spell mixed with a liquid [tes, oil, lotion, bath, brew so on] as long as you sit and charge it with energy, it can be a potion. i know some people who charge energy into soup and call it a potion. even though i had some potions [like love potion number 9] i started with teas, then bath salts, i sort of specialize with them. oils are probably the hardest, though i've yet to try making a lotion. there' two ways of making oils, the harder is when you heat the oil to infuse the herbs. the trick is not to deep fry them. for me, all the oils i tried making this way wind up smelling like pumpkin XD [for some reason i smell pumpkin when somethings gone bad or gone wrong, don't know] the easier is more time consuming. take some oil and the herb or herbs. place them in a container [mason jar would work] shake and place in a cool dark place. every 24 hours shake it again. each week, drain the oil and put in new herbs. repeat for about a month. some people will say a chant while shaking the bottle, but it's up to you.
potions are fun, but there's a lot to them. pick up some books, Scott Cunninghams Incense, Oil's and Brews would probably be your best bet. really good resource. I picked up this one book Magick Potion by Gerinda Dunwich, it's more historical than actual recipes, but i like it.