Each software package has their own set of instructions; how to up and download files would certainly be a part of that. The 246T sticky in the Uniden forum, plus the Yahoo groups I mentioned in a previous message, would be the places to go for such information.
I think what's confusing is the term 'trunking file'; what you are really looking for is a data file - be it from a UASD Uniden format, ARC246, ect. that contains the information for trunking in your area. And yes, that is as good as any a way to get started. That way, you could start editing and changing the file to the way you want it, and along the way, you'll start learning. It seems to be common, by the way, to upload files to the state's forum; there's no special place for them. However, only certain file types are permitted. I've done that quite successfully in the DC forum, for example.
The 246 is a brand new animal in the scanning world; dynamic memory and 5500 channels (sans alpha tags, it's a bit less using them, if I understand the usage correctly), and to be honest, I'd never start someone who is a newcomer with that scanner. It's just too much. Hopefully there are other Oklahomans that can jump in and give you what you need. Nothing like local help to get you over the hump.
73s Mike