The active file is the one that your changes are saved to. If you don't specify an active file, a new plugin will be made. In your case, what you did is correct.
There is a difference between the ID of cells and their display name. It may display as "Your Farmhouse" in-game but the internal ID may as well be Doombuggie41FarmhouseObamaIsACommunist41.
I'd recommend loading up Rorikstead itself and clicking on the teleport marker, but chances are you don't know how to do that either.
Nope I don't, but I am having the CK tutorial with me now so I guess i find out soon, another question, I only want to take the interior of this mod and maybe the house itself to a new location(a little bit south of Riverwood), and make the place where it stood(east of Rorikstead) just like vanilla agian, so to prevent conflicts with later mods, is it possible to just select the interior of a house, without the rest of the mod. The mod of which i am basing it off is also has a mill with some things in it which I want to completely remove.