Read ALL of the instructions before playing... Click the recipe book to open the Potion Making recipe book. Press the v key to look at the ingredients needed for Veritaserum. Press the l key (L lowercase) to look at the ingredients for Liquid Luck. Press the h key when you're done looking at the recipe at the moment. Click the purple "Ingredients" button next to the book to select an ingredient to put into your cauldron. Once you click the button, a purple page with ingredients on it will show up. To make it go away, press the space key. To choose an ingredient from the purple page, press the corresponding number. For example, to put in powdered moonstone, press 3.
By the way, the recipe book for the potions doesn't have the accurate ingredients and things in the Harry Potter books and movies; I just made up the recipes. There are two potions you can make: Veritaserum and Felix Felicis (Liquid Luck). This project took me 1 1/2 hours to make Credit for the Harry Potter theme music goes to @ivypool2 Credit for the dark purple cauldron sprite goes to @hetingfei