what is polyurethaine and sealer? Xenical to make it darker what are we suppose to do?

i need to know how to refinish my hardwood floor, it looks simple, but I’m figuring that it must not be , since the companies that offer this service charge so much……i already have a buffer somebody told me prescription medications online all i have to do is attach sandpaper screens ……sand…..then apply polyurathane……..does anybody know

We recently had our hardwood floors refinished by a friend of a friend who said he knew what he was doing. The floor has dents/waves in it and the finish is not smooth but online pharmacy prescription drugs has small pimply bumps on it. Is there any way to fix this without refinishing the floor entirely? We haven’t paid this "friend" yet – what should we do?
The dents/waves were not in the floor before it was sanded. Could the sander have caused them? Is there a way to fix without resanding all of the newly applied stain and polyurethane?