If you own the domain names ggexample.com, ggexample.net and ggexample.org and you want it set up so that when someone types ggexample.net or ggexample.org into a browser the visitor is automatically taken to ggexample.com (and the .com domain remains in the browser’s address bar), that is commonly known as a “domain forwarder,” or “domain forwarding.”
Traditionally domain forwarding is done at the domain registrar level. To set that up, contact your domain registrar and they can show you how to forward the domain(s) to your primary domain using their system.
Alternately, if the domains you want to forward were registered through GreenGeeks or are otherwise controlled in your GreenGeeks cPanel account, you can set up the domain(s) as “Redirects” and they will forward to the primary domain.