If you want to keep your information safe online, you should use a different password for every account you create. However, it is almost impossible to remember all these passwords, so most people use the same password for some or all of their accounts.
You can have the best of both worlds: the security of multiple passwords and the convenience of having only one password. LastPass is a secure program that stores all of your passwords in one account. The installation process is painless, and every time you create a new account afterwards, LastPass will store it and automatically fill in your login and password information the next time you access the account. It can even scan your browsers for currently saved passwords.
Of course, this program is safest on a computer that only you can access.