When you make a video, you normally shoot a bunch of clips and photos, pick the ones you want, arrange them, add music and other stuff, and then publish it.  
iMovie has a special feature that kind of goes in the opposite direction.  It’s called "movie trailers", and looks like coming attractions for a movie.  iMovie has a template with the story line already set up, background music, and a theme.  There are many many boxes that are labeled for what iMovie wants you to put there - short video clips, photos, etc.  Once you’ve dragged and dropped everything they ask for, you push "go" and it churns out your movie.  Here’s my first try at it:

https://youtu.be/7eXss4Z9FM0

Great info - thanks for that!

Really good information. Thanks for sharing.

Posted video here for you

4WDaus Posted at 2018-1-20 02:06
https://youtu.be/7eXss4Z9FM0
Posted video here for you

Thanks.  When I first did my posting, my video had been marked as "Private" on YouTube.  The link stayed the same on this forum after I fixed that error.