Security questions are an added level of protection. They are presented at login, and when you try to change contact information or key access credentials, like your password.

These are “out of wallet” questions to protect your account from unauthorized access.  If someone stole your wallet or read your Facebook account, they should not be able to answer these questions.

Once you have completed the security set up, you can choose "Remember me on this device" to bypass the security questions during future logins.  However, if you login from a new device, or have cleared your computer's cookies, you will be required to re-register your device and answer the security questions you have created.