I don't know why you think you can't see anything. I can clearly make out the structure and the little dots around them are fish of different sizes. Could be crappie, bream, or bass as they like structure.
If you look at your depth you can see they are 20 feet down so that little dot at 20 feet would be about 10-15 inches on the surface.
The Di shows the dots as fish and the 3D view shows the curved signature of the fish. If you look they are curved which is how the air bladders in the fish show up on sonar.
My Humminbird can be set to ping when a big fish passes under the cone. Don't know if you can set yours as it looks like a Lowrance but try to see if the unit can distinguish between big and small fish and let you know somehow.
That stuff is not trash but fish. If you see a ball of dots then it is a bait ball and bigger fish will be close by usually.
Don't discredit those blips until you check them out thoroughly.
USAF Retired and Fishing!