What is GSX (located at gsx.apple.com)?
It appears all your questions are answered by the About GSX link, which includes the requirements for accessing GSX. If you take a moment to read that info, your questions will be answered.So could I as a person alone (i.e. not with a business) order parts for my self to repair my computers?
Possibly because you're not logged in.I still don't get it. Also, both the Quick Start guide and the User Guide lead to 404s.
You need to work for a service provider or be part of an institution or organization with a self-servicing account.