Using a computer is a never-ending struggle to keep track of passwords for email servers, file servers, websites, and other private information. The Keychain Access software (path: /Applications/Utilities/Keychain Access) automatically stores passwords from Keychain-aware applications such as Mail and Safari. Users can also manually add their own passwords to the keychain. Later, the keychain can be unlocked to reveal the original cleartext password. Keychain also manages digital certificates—virtual documents that are used to authoritatively identify servers and individuals.
By default, all users have their own keychain named login. This is called the User keychain. Additional User keychains can be created to store specific information, such as credit card numbers, PINs, and so on. Think of the keychain as a database of your most sensitive information, all accessible through your account password.