Nobody likes commas: they're weird and confusing and possibly pointless. My brother decided to boycott them entirely in his senior year of high school, leaving his lists running together and his appositives undefined. Even veteran copy editors sometimes struggle with where exactly to place these reviled punctuation marks.
Even so, if you want to succeed on the ACT English, you'll have to learn how to expertly employ commas. The good news is that there is a fairly limited set of comma rules you'll need to know for the ACT. But before we get into the nitty-gritty technical stuff, let's establish one very important principle.