Code Commenting

All programs should be commented in such a manner as to easily describe (in English) the purpose of the code and any algorithms used to accomplish the purpose. A user should be able to utilize a previously written program (or function) without ever having to look at the code, simply by reading the comments.

Commenting is the "art" of describing what your program is going to do in "high level" English statements. Commenting is best done before actually writing the code for your program.
This video describes the importance of code commenting