A spell is basically a ritual. It's something you pour your energy and intent into, in the hopes of getting a magical result.
There is some forums and articles on how to make a spell, spells can be simple or complex, either way. Also potions is like teas, oils, and so on.
Learn what is magic and the basics of magic before you start casting spells and look around in the articles, forums, or other websites to help you out.