At Stalingrad, you would have mostly seen early T-34 tanks. Germans, StuGIIIB, Panzer III and Panzer IV, probably D and E.
The primary German Unit at Stalingrad was the 6th Army, although other units were involved with trying to clear a path for a German breakout. I would suggest doing a google search on Stalingrad and you'll find all kinds of information. There are also some excellent books about this epic battle, my favorite being "Stalingrad" by Anthony Beevor.
A seam is the join line between two parts. When you glue two fuselage halves together, for example, there is a seam where the two parts join together. Unless it's supposed to have a panel line there you'll want to fill it with putty, super glue or some other material, and sand it smooth so the seam is no longer visible once you apply paint. Some of the most common places for nasty seams are along fuselage halves, wing roots (where the wing joins the fuselage, those can be particular tough to deal with as there are often complex curves here, and you don't want to get carried away and sand away panel lines that are supposed to be there), along cowlings and lately, with the modular design of many of the new kits, there will be a nasty seam going around the fuselage where the tail section joins the rest of the fuselage.