The User Log-In component authenticates users of the site, and can provide the ability for visitors to self-register.
The User Log-In controls access to all parts of the website by matching the user against the permissions set for them by the site creator.
The Behavior Editor of the Log-In component gives the designer control over all the available controls, including the requirement for new registrations to be validated against an email address.
A common requirement is for visitors to a website to register before they can access part of the site or some particular asset.
The method for enabling new user registration is explained here: Allowing User Registration