To be able to use the n command you have to first search for something.
So after you do a search, the cursor will stop at the first next match. If you hit the n key, and there's another something, it will go to the next something.
Basically does the same thing but instead of moving forwards to the next result it will move backwards to next result when typing the n command.
This command will go backwards as well, or more precisely, the opposite direction depending if you used / or ? how you did the search.