Commas can sometimes be tricky, can't they? Typically, a comma comes before "but" when it's connecting two independent clauses, like: "I wanted to go, but it was raining." If "but" is followed by a simple phrase or word, you often don't need a comma: "It's small but cozy." Do you have a specific sentence in mind where you're unsure about using the comma? I'd love to help you with it!