Judging and naming questions?

[Djarum Black]

Could someone who does AOS judging or actively shows plants help me understand how this works please? I have been to both the AOS website and to the British site but I just do not understand how this works.
Probably a bunch of dumb questions but here goes...

If I wanted to show a plant that was given to me by someone else a while ago (more then 2 years) how can I do this? It is the naming part as well as which plants can be judged that confuses me. If it has no cultivator name does it need one before it can win anything? Also does this mean I can name it myself? I have permission from the previous plant owner but that's all. And if other plants exist from the same breeding that are already shown and named, does this mean I can't have mine judged and named?
As you can see I am very lost.

Now as far as seedlings that I may have crossed myself and grew, do I have to register them before I can have them judged also? If the cross was already made does that disqualify them from judging/naming?

I know this is many questions and I as said, I have read many different articles and I've even been to the registering sites, but I guess it still all looks like Greek to me. I just don't want to put the cart before the horse so to speak.