You could start by re-reading those sections in your book and those pages in your class notes. Then read the explanations in a few other texts, and study some online lessons (found by using a search engine, etc).
Then try re-working a few homework exercises or textbook exercises for which you have the answers in the back (so you're sure you're getting the right answers). Then think about how you'd describe what you're doing to another student.
Write out your description.