Recursion is a fundamental technique common in mathematics and computer science. If you don't have a background or you feel yours is week then check this out: Introduction To Recursion
We will be providing quizzes on recursion, this is our first one. Get yourself started and try it. Quizzes difficulty will start from focusing on simple recursive functions ending with complex functions so by finishing our quizzes it's pretty likely that you will be ready to start leaning Dynamic Programming and writing Backtracking solutions.
If you felt this one was really easy, you can try the harder one: Quiz: Recursion (Hard)