No user error, I also realized once I submitted that it was kinda hard to figure out!
The idea is that when you put something into the cauldron (by right-clicking) you gain the effects of the potion made by the ingredient you put in (Example: Herbs make speed potions). While it's in the cauldron, the effect is applied to you, but you can take the potion out of the cauldron to use it on enemies!