That's a very nice unit. Should be a manufacturer's tag with name and model # on the unit. Look for a operators manual online.
Get some practice using it on good working items like table lamps, table radios, and electric motors to familiarize yourself with it. I often use a Variac on my drill press to really slow it down when drilling large holes in heavy metal.
The isolation transformer is often used for working on old radios that have hot chassis. Still has value today if you start using test equipment.
Hope you can find a manual for it. I haven't been in the hobby long, but haven't seen those threaded three pin connectors before.