...

You never have to register a domain name. Some groups don’t sign up for a domain name because of the expense. And that’s okay. You can use your hostname from RescueGroups.org as your domain name.

My organization already has a domain name registered, can we use it?

 Yes.  To To do that, you can add the domain to your RescueGroups.org account, and “point” your existing domain name to our default name servers. This will allow your visitors to use your existing domain name to access your RescueGroups.org Website so that visitors see your domain.

See the instructions for Using a domain name you have already registered.for Adding an existing domain to your account

My organization would like to register a domain name

...

• You can register a domain name through our service and we will point it for you. See the section Registering a Domain Name.
• You can register a domain name elsewhere and point it to your website. See the instructions for  Using a domain name you have already registered .Adding an existing domain to your account

Domain renewal and your Website Service

...