You need to first use an ingredient to make a mundane potion ( or something like that ), then you start adding other ingredients to make different potions , then if you want better potions add other ingredients.
I think the base ingredient is Nether Wart , go in the nether and make a farm.
1: Make brewing stand
2: Make bottles
3: Fill bottles with water
4: Place water bottles in brewing stand
5: Use nether warts in brewing stand
6: Use [ingredient] in brewing stand (try sugar)
OPTIONAL 7: Use redstone or glowstone to increase effect of potion
OPTIONAL 8: Use gunpowder to make them throwable
9: Enjoy potions