I don't pretend to be a fishfinder guru but here is what I've learned. I'm not saying these are the best settings and I'm sure it can be dialed in even better. In general, there are settings that will almost always stay the same and some can change depending on the water properties of where you fish. I have noticed that the sonar data is less useful as you get shallow (less than 5 or 6 feet) so no matter what settings you use, the screen will be a mess. The first time you use the fishfinder, expect to spend most of your time staring at the screen messing with the controls and not fishing.
Here are the settings I always use:
Sonar=>Fishing Mode=Shallow water
Sonar=>Sonar Options=>Fish ID=Off
Downscan=>Frequency = 800kHz
The following can change based on where you fish or even day to day on the same lake if conditions change. A change in one can affect the others:
Sensitivity=72 I think this is the one that you should change last after the others. There's no "right" setting, only a setting that you are comfortable with. Lower the sensitivity and your screen will clear up but you could be removing some data you want to see.
Noise Rejection= Off
Surface clarity=Medium One source I saw said that surface clarity of Low is for murky water. For clearer water, try Medium or High.
To get the display so that the frames are on top of each other:
Pages screen=>Hit "Menu"=>Page split
One important thing that I didn't learn soon enough was how to control a particular frame when there are multiple frames. When you bring up the pages screen, it will have a message that says something like "Press Pages button to make the Sonar active". That means that if you are showing downscan and sonar, display settings like zoom will only impact the downscan portion.
On YouTube, search for Lowrance sonar videos. Don't get too specific by searching for Hook 4 because there aren't many dedicated videos out there.
Everything I've read or seen says that bass relate to the bottom most of the time. If the fish on your sonar are stacked vertically, that's probably crappie, not bass. BUT! Don't trust your fishfinder 100% and the only way to find out what's down there is to catch one.
Here's a screenshot from this weekend with the settings I listed. I need to point out that the only fish I caught were extremely shallow and the fishfinder didn't have anything to do with it! It's a tool, not a magic bullet.