PasswordPress is an application that helps you determine what your next password should be.
However, PasswordPress only makes new passwords for you. It doesn't store passwords anyplace; it doesn't remember what password it gave you last.
You know it is important to have a good password for a variety of things (software, cell phone, bank card, etc.). However, most of the time, if you use something that is really easy for you to remember, it is something that is very easy for someone else to figure out.
On top of that, your password is something that should be change periodically (just in case). How are you going to create a password that isn't too easy for someone else to figure out? That's where PasswordPress comes in.