Side and down scan can definitely be hard to interpret but one must always look to see if shadows are there helping with the explanation. The shadows may often be what provides the most information.
One problem I always used to have was I would go thru the manual and read about each of the adjustments that were possible. I would get so wrapped around the axle that I would convince myself that I couldn't possible remember that much.
Then a good while later, a YouTube video really helped me out. It said when you first setup a fish finder many of the necessary changes only need to be made once. With those, there is often a startup guide that I'll take you thru what is needed. Set it and forget it. After that, there are a small number of adjustments that each each category like sonar, navigation and so on might need. The sensitivity may be fine for a good while but then the water gets muddy and there is too much clutter on the screen. It generally just needs a slight tweak, maybe three clicks one way or the other. Learning this taught me that even though I was just a simple country boy, I could actually learn to use these things.
The newer units often have several setting that can be set to automatic and the companies have gotten the automatic setting very close to what is needed.
Anyway, you can't learn how to make adjustments without actually doing it. repetition will last longer than just doing something once and moving on.
There I go again, it is 1:38am and I can't help but write a book. sorry
tight lines