Guys, thats a Humminbird 898SI with a broken screen that I didnt want to pay $300 to have humminbird replace so I picked up a screen protector (which happened to be for an iPad) and cut the screen protector down to size. I was just trying to keep the water out and prevent further loss of glass.
Newbeans,
Typically, anything you find on the bottom near the reefs will hold fish of some sort. I am not good enough to look at that screen and say what it is, but I know something is down there. Start with small bait and see what hits. If you start pulling in a pile of the same fish, then you know what is schooled down there.
It also depends on your fishfinder. Some are much more detailed than others. I floated over a piece of bridge before and could see each piece of the bridge girder. I have also floated over a dingy and had a perfect boat outline show up on the screen. Takes time and practise to get it tuned in.
Nearshore reefs, my strategy is to find a school of bait fish, catch a few and use them as bait on the bottom. Either cut or whole, the predators will come by and pick them up. While I wait I keep catching bait. Keeps me occupied.