A square buff sander has a rectangular base that vibrates in multiple directions and uses multiple grades of sandpaper to sand and finish a floor. A drum sander has a sanding belt that does the work, but is more difficult to use, especially for beginners.
To use the square buffer, start with the coarsest grade of sandpaper and move the machine slowly across the floor. Check the sandpaper periodically, and vacuum the sawdust to check progress on the floor. Gradually switch to finer grades of sandpaper until the floor is smooth and uniformly sanded. The square buffer head can get close to the edge of the floor, which means very little, if any, hand sanding is needed.
The drum sander's belt is more aggressive than the sandpaper and pads of the square buffer sander. If too much time is spent is one spot, the belt could gouge the floor. The floor must also be sanded in the direction of the grain to avoid damage.
Drum sanders come in two varieties: the tip sander and the level sander. The tip sander is easier to learn and has two wheels on the back that are tilted up to make turning easier. The level sander mechanically lifts and lowers the sanding drum. Starting drum sanders with the paper off the floor keeps them from immediately dragging the user around the floor when the machine is turned on.