Hi, Barb. You have the process right. Check at a couple of spots until you have the whole hardwood floor uncovered. It is unusual to see anyone put plywood over the floor before carpeting so I wonder if there was something that they were trying to cover up, like pet stains.
Honestly, you can refinish your floor yourself but it is a big, nasty job. Before you embark on this, I really suggest that you get a copy of the November, 1999 issue of The Family Handyman magazine and check the article on page 52. Call 715-247-5060 for availability. It is not a bad idea to do this even if you plan to have it done so you get an idea of the process that the pro's will use.