This feature allows you to configure your site for your own domain name, and to setup email flow using your domain name.
First, let's review some terms that will be helpful to you:
Primary Domain - This is the main domain name to be used on your website. It should be the domain name you wish to advertise.
Alias Domain - This is a secondary domain name that could funnel visitors to your primary domain name. Examples would be a .org pointing toward the .com domain name. When visitors type in domain.org, they would actually explore your site on domain.com (assuming domain.com was your primary domain name.)
Parked Domain - This is were there are two parallel names to access your website. Both the primary and parked domain names would point to the site, and be independent of each other. Parking has the downside of dividing your search engine traffic among the names parked.
Redirect - You can set an aliased or parked domain name to redirect to a specific part of your website navigation. When someone visits your website home page using the redirected, parked or aliased domain name, they will be immediately redirected to the subpage you have selected in the redirect settings.
Go to your website, click in the admin bar "Settings" and then "Domains and Email". You will see all domain names to your site, and you can add a new one.
Before your domain name will link up, you will need to set the domain name name servers to these settings:
Once this is complete with your domain name registrar, you will be able to park that domain name to your site. You can also manage your email settings to point your domain name to an email provider of your choice through the manage email settings area.