While recursion is a difficult concept, Codecademy interactively walks the user through a set of lessons that start with the most basic of loops and end with some practical examples of recursion implementation. As someone who has been using recursive algorithms regularly over the past three weeks (Hack Reactor’s curriculum definitely does not shy away from the concept), I wish I had come across this resource sooner. However, it was still an excellent review for me, and I plan to take my strengthened comprehension of recursion and apply it to some of the more difficult recursive problems, such as those involving permutations.
For those having trouble following a function through multiple levels of recursion and determining the order of calculations, you are far from alone. Coming up with a visual representation of the problem can help, and walking through each step methodically and predicting what the program will do at each point is also a good idea. Good luck!