I have a good number of resources that I use when preparing our students for Mill and Lathe training.
My personal favorite machining introduction is the educational series by Smithy Industries on YouTube. Playlist below.
https://www.youtube.com/playlist?lis...88EC2A1583EED2
Do keep in mind that I have great dislike for 3-in-1 machines and feel that you money is better spent on bigger more cost effective machines. However they do a
fantastic job of explaining the common machine features shared by all lathes and mills, as well as the basics of operating them. Yes, it's not a Bridgeport walk-through and tutorial, but most of the features should easily carry over to the hands on stuff.
If you want some very in depth machining and shop walk-through's check out
THATLAZYMACHINIST's channel on YouTube, he does a great if long winded job of thoroughly covering various topics.
Some others that should be useful to you are
Toms Techniques and
mrpete222. Also useful is
Clickspring, the work he does is informative, highly detailed, and artfully awe inspiring. The things he creates makes the stuff I do look shameful in comparison.
Outside of what you can find in there, just use some pictures and go over what the various parts of the BP are called and what they do/used for. The machine is easy, using it effectively and efficiently will always take practice. Does it/they have DRO's, belt head or variable speed, what features are you going to teach them to use?