Demolition takes out the tub, the surround, and usually the wallboard behind it. Then the plumber adapts the drain from the tub's position to the shower's, sets a new valve if needed, and the work is inspected before walls are closed. In the 1980s homes common here, the drain is often plastic and easy to adapt; in the older minority of houses it may be cast iron, which takes more care.
Your contractor files the permits with the Lakeville Building Department, usually online through Viewpoint, and calls for the plumbing inspection at the rough stage. After that come the waterproofing, the base or tiled pan, tile or panels, glass, and trim.
Because demolition water and grout rinse drain to your own septic system, ask the crew to bag thinset and joint compound waste and rinse buckets outside rather than in the tub.