Sonar Screen adjustments

I have a 917C unit that I am still learning how to fine tune.
I have a couple basic questions. How and where do I adjust the sensitivity? What is the best or ideal sensitivity setting? I saw a video that James had where a screen shot of the huminbird unit had a black background. is there an advantage to do this? how do you change the background. I also saw the bottom display had the depth, GPS speed and time along the bottom of the screen. how do set it up that way? On the GPS side, how do I change the color of a new trail? if I wanted to view muliple trails in the same area. e: gray for day 1 magenta for day 2 etc. and/or delete a trail? thanks Dave C.

Do not misunderstand I wish I had your answers in my head to assist you but, I do not.
Have you tried to read the manual yet?

You need to go into the settings and change user settings to advanced first. Then you can change display settings around. To change the backround, hit the power button once. pick your color. Sensitivity will vary based on depth and bottom content.

you have to sit in the boat..either on the lake or the garage and play with the thing..no short cuts you have to use it to get comfortable..you’ll be amased at the info you can see with pratice