A barrel blank is a 30" long, 2" thick round stock with a hole drilled down the center and then rifled, in virtually all cases, by hydrolically pulling a hardened carbide "button" with the negative of the rifling on it. As the button is pulled through the bore, the metal is forced around it and forms rifling.
In order to make a finished AR barrel, you need a lathe to turn down the barrel that's at least several inches longer than the final barrel length will be. You will need to "profile" the barrel (turn it down to desired thickness in various areas), thread the chamber end for a barrel extension, optionally thread the muzzle end for a muzzle attachment, and most critically, cut the chamber to precise dimensions based on the barrel extension. An alignment pin hole must be drilled at 12 o'clock on the barrel (based on the orientation of the barrel extension's feed ramps), and likewise a gas port must also be drilled. If you wanted the barrel chromed, it would have needed to have been chromed before drilling the gas port.
Wilson generally doesn't sell completed barrels at retail, but will make them if a retailer orders a big enough lot. Normally, the manufacturer/retailer does all the finish work, or farms that out to another machine shop.
-Troy