No mystery to it. Here is exactly what happens from the moment you call to the moment we hand the job back.
Wear layer, board condition, subfloor soundness and moisture content are checked. Sanding and finishing a floor that is still wet from a leak locks the problem in.
Furniture out, base shoe removed if the edges are being taken tight, vents covered, and doorways sealed with plastic and zippers to keep dust out of the rest of the house.
Coarse grit to flatten and remove old finish, then successively finer passes. The edger handles the perimeter and the two have to be blended, which is where skill shows.
Applied and wiped back consistently, then given full manufacturer dry time. Rushing this is the most common cause of a finish that will not cure or that lifts later.
Two to three coats with light abrasion between. You can usually walk on it in a day or two in socks, but furniture and rugs wait considerably longer while the finish reaches full hardness.
None of this is required — it just makes the visit quicker.