I have refinished a couple of oak wood floors in an old apartment building, and also one in a newer building. The procedure is the same. I rent a “drum type” floor sander with various grades of paper. Be sure to work in the direction of the grain. I then finish the edges with a circular “edger”. There is a square orbital floor sanding machine available at most rental places, however I find this does not strip the old varinsh efficiently. I would recommend this machine only as a follow up stage to the drum sander in order remove any machine marks. (If you would like a furniture-like finish.)
Last but not least, apply two (or more) coats of polyuerethane lacquer.

Desmond J. Henry.