When installing drywall, does one hang the ceiling material first or the wall material first? Or does it matter? Please explain.?

Ceiling first. Then wallboard on the wall provides some support for the ceiling at the edges.

Ceiling first, then the walls. That way you do not have to fill the ceiling to get it flat. It is much easier to fill gaps at the top of the walls on the vertical. But if alone you can do the walls first with a gap at the top to slide the ceiling pieces in. The main thing is that the ceiling pieces go out to the studs and are covered by the walls.

Also the walls support the edges of the ceiling.

On the job I've seen it both ways, just bear this in mind, it's easier for amateurs to fill gaps on the vertical, so fit the ceiling tight to wall studs.

If hanging alone I do the walls first, leaving a 5/8" gap at the ceiling to slide the sheet into provide an extra hand to hold the sheetrock up when I do the ceiling.

I guess it depends on the structures size and

What type floor and ceiling in the room. So

It may not be the same for every construction.

It doesn't really matter, but most people want to "be done with the hard stuff" and do the ceiling first.