A performance review period is a time when your manager reviews your work and tells you where you need to improve or where you have been doing well. Some smaller companies do not have a concrete review process. But large companies have a process in place. Some of them do a review two times a year, and some companies have a yearly review. Your review is sometimes dependent on how much raise you will get and sometimes even the bonus amount.
Because the review is different from company to company, I will use this English lesson for sentences you need to say during the time you speak with your manager. I will not be going into the details and timeframe of the review.
If there is a process in place, then you probably have a template to write down your achievements over a certain time span. This is your chance to toot your own horn. So include everything you did and do not be modest. If you don't have a template to follow, then write down on a word document the achievements you made. It is also good to write down some places where you want to improve. Some people might think that telling your manager where you need to improve is basically admitting to having flaws, but great managers think a person who can identify their own problems and fix them are great employees.