It's an old unit, low resolution, needing to be replaced. If it's working properly and sensitivity isn't set too high the screen shouldn't have lines cluttering across it. If it does that with the outboard off, the head unit or transducer is probably defective. You should mostly see open water, some specks indicating debris or fish, and bottom with structure down to about 150 feet, or bottom only down to about 400 feet. Open the MENU and look for a "factory Reset". I'm not familiar with that unbit, so can't be specific. A reset will put the unit back to recommended settings for average water conditions.
You bet, time on the water is simply required to learn to use sonar. If you can find clear water and see a stump, position the transducer over it to learn what a stump looks like on screen. Study how weeds appear. A light-contrast bottom is hard rock, while a dark bottom is mud. Check out the links I posted some time ago. They will help you a lot. Jim