If you do not own a graphing calculator and you cannot use an app on a smart phone, this link will carry you to a free online tool. There are many others and they are fine. This is just the one I have been using for a few years.KHAN Academy
A great website for tutorial videos and extra practice.Mometrix Media LLC
This is a great ACT prep site (for all subjects). The company provides free instructional videos for every content area on the ACT test. They will try to sell you a review test or their version of the flashcards but if you need help with a specific topic, this site is wonderful.