Comments are some piece of English text which explains what this code does, we write comments in the code so that is easier for others to understand. A comment line starts with # , everything after that is ignored as comment, that means they don't effect on the program.

>>> #this is a comment
>>> #the next line will add two numbers
>>> a = 12 + 34
>>> print c #this is a comment too :)

Comments are mainly for the people will develop or maintain the codebase, so it means if you have some complex code somewhere you should write enough comments inside so that anyone else can understand the code by reading the comments. You can also use some standard comments like

#FIXME -- fix these code later
#TODO -- in future you have to do this