how do you copy and save sections of a movie with out changing the original movie

Project Assets panel in Expert View maybe.

Perform splits into sections of original and copydrag to Assets Panel, which will not change original file, it remains as it is on disk.

Or just reorder clips as you split them in timeline.

A clip is a reference to a source file, and start and end offset in that file.

So if you reorder clips in timeline, sourcefile does not change like that.

You could even start another video track and disable original video track later.

Handy to drag clips from one track to another.

And do save as or save as copy of a project and continue do individual things with each.