Do you have several passwords, and you're having a hard time remembering all of them. Writing them down on a piece of paper is not secure. You could created encrypted document of some type (e.g. text, Word, Excel, etc.) to store them. There are also several password management applications available for you to download, some are free and others cost money.
Although before you pay for anything or try other programs. Check out a program called KeePass. This is a multiple platform, open-source password management application. There are also 3rd party ports of the application that work on the popular mobile platforms (e.g. iPhone, Android, etc.).
KeyPass will store your passwords in an encrypted file, so even if someone steals it they can't read it unless they know your password. Check out the web site for more information.
If you want something that offers more features then KeyPass, checkout some commercial password management applications like: