Comments are parts in the program that are used to inform about the way the program works. They are not going to be compiled, nor will be exported to the processor. They are useful for you to understand what a certain program you downloaded is doing or to inform to your colleagues about what one of its lines is. There are two different ways of marking a line as a comment:
Tip When experimenting with code the ability of commenting parts of your program becomes very useful for you to "park" part of the code for a while.