The basic idea of a screw-propelled vehicle is simple enough: instead of wheels or tracks, you build a vehicle with a pair of, as Wikipedia puts it "auger-like cylinders fitted with a helical flange." To make that a bit easier to understand, think of a machine that literally crawls along the ground on a pair of giant screws. To turn you use the same method a tank does: one screw either gets locked in place while the other one doesn't or, to make a 360 turn, turn one screw one way and the other ... well, the other way.
The article comes with a collection of some beautiful photos of this weird mean of transportation in action I bet very few of you even knew existed. Yeah, me neither.