Anyone know how to refinish hardwood floors?

First question is whether it needs a full sand or just a recoat. If the finish is dull and scratched but you're not down to bare wood anywhere, a screen and recoat is a weekend job - clean it, scuff the old finish with a buffer, vacuum, new coat on. Full refinish means a sander. Hire an orbital floor sander if you've never done it, a drum sander will dig a dip into the floor the second you stop moving with it running. Go with the grain, work through the grits without skipping any, vacuum and wipe down between every coat. If it's engineered board, check how thick the top wear layer is before you sand anything, some only take one light sand in their life. Oil based poly goes amber over time, water based stays clearer and dries a lot faster.