Facebook Requests are an easy way to let your user's invite their friends to any page of your site. They also allow you, the site owner, to send updates to any, or all, of your users about new blog posts, events, sales, or whatever you want. The requests are sent through Facebook and appear as either friend notifications or application notifications, depending on how they were sent from your site. Below is a description of each, and how to set both up.
It is recommended that you have an SSL certificate installed on your site for Facebook Requests. Facebook will not pass some user-identifying information about who is accepting the request without an SSL certificate on your site. You can use the Requests feature without SSL, but requests may not be marked as "Read" properly when a user accepts them.
For more information on setting up SSL on your site, see our Obtaining SSL Certificates for Facebook guide.