Standard Schwalbe winter tires have studs where the tire is always in direct contact with the ground. Schwalbe Marathon winter tires have another set of studs offset to the side of the treads.
Are studs worth it? It depends. If you're regularly on ice, maybe. If you're on packed snow, or concrete, etc, they'll actually slow you down (and make a lot of noise), a good tire with a little bit of tread, at a slightly lower PSI than max, in our experience, works best.
If the bike lanes near you have anything other than packed snow, or bare asphalt, let your local city councillor know, shouldn't be like that.
If you're only getting one, put it on the front.