Comments are lines of codes that don't execute. Generally, they are written by the author of the code. We need comments because we can't express ourselves all the time. But make sure that you don't write bad comments for example if a line of code does multiplication 3 * 5 it's obvious and its bad practice to write a comment for this line.
Always try to write code that explains itself so you wouldn't need to write comments. Of course, there will be comments all the time, even for you as the author of the code. Sometimes you will have hard times to understand what a part of the code does. Then comments will help you to understand it quickly.
Enough to say, now let's see how to write comments in python:
>>> # this is comment line
...
>>>
Anything starts with # is ignored by python.
>>> # x = 8 ** 2
... # y = 6 ** 2
... x = 55
>>> x
55
>>> y
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'y' is not defined
If you want multiple comment line then put # in front of every line you want. As you see we defined y in the comment so when we try to get value y it gives an error because comments don't execute.
The most important thing about comments is to write them when it's hard to understand the code or if you can't express the code more then you did. Use meaningful names for variables.