Most people have multiple passwords in their computing lives. Apple helps you manage your passwords, account numbers, and other confidential info through keychain. Mac keychain is a feature that stores passwords for programs, e-mail accounts, Web sites, and more.
You can create keychains for different purposes (one for online shopping, say) by opening Keychain Access in the Utilities folder under Applications. Your keychain password is initially the same as your login password, and for many users that’s the way it’ll stay. To add keychain passwords, choose File→New Password Item or click the + at the bottom of the Keychain Access window. Fill in the account name, keychain item, and password. Apple will let you know if you’ve chosen a wimpy or bulletproof password.
If you’re using just one password, shame on you; security experts think that’s not such a keen practice.