The "Security Roles" enables the Administrator(s) to configure what each member or visitor will have access to within your community website. The security feature uses "Access Keys" to configure each option. When setting up a module's security options, any Access-key that is selected and moved to the "Selected Keys" option box is what is permitted on your website portal, anything under "Available Keys" option box are the other Access-keys in your system that are currently not selected by the site Administrator to affect the given module within your website portal. Any members that have the access-keys assigned to their site-member account that is in the "Selected Keys" section will have access to interact with the given module.
By default any member has access to the whole user interface (general public-side of your website) and any visitors has access to everything besides posting content to your website.
The "Everyone" access-key can not be removed (deleted) from the system as that key is used for any visitor that is browsing your website. Also the "Administrator" key can not be removed from the system, because it is used by the Administrator(s) on the website so they have access to the entire portal system.
For detailed information on what each question is, then please navigate to the "Modules" section of this module