I am going to be trying out the PTR. I really dont know how it works, but I have heard others talking about it and wondered how many of you are there and if so, servers, names, etc...
Is it possible to form a guild on a ptr?
It's basically another instance of WoW. Nothing you do there will be carried over to the live version, but you can have characters transferred from the live version to the PTR. The purpose of a Public Test Realm is to test out changes being made in future patches to the live version, so yes, anything you can do on live you can do on the PTR - including create guilds, run instances and even (I think) browse the AH.