Yes, the bilge is a small section of the hull at its lowest point intended to collect water that may get into the hull. Where does that water come from? Sea spray, rain leaks, fresh water tank plumbing leaks, galley spills, wash down water, wet swim trunks, etc. Besides the bilge which is visible there are likely some gallons of water trapped in the hull stringers below the sole. Boat motion or heeling may release some of that water into the bilge, The small electric bilge pump is a convenience item rather than a safety item. It is just an easy way of discharging overboard that incidental water found in the bilge rather than having to scoop it up manually. An automatic bilge pump or one with a float switch is one that will discharge water without supervision or interaction. A lot of boats came with manual switches back in the 80's and that is fine too. Flip the switch when you first come aboard and a few times a day while underway. It is not the function of the bilge pump to prevent flooding damage. In order to keep the boat dry any leaks must be found and corrected, Thru-hull valves must be inspected regularly as well as all the hoses and clamps. Most bilge pumps range from 500 GPH (gallons per hour) to 1,000 GPH. Logic follows that the smaller boats should have the larger pumps as they will fill up faster. These pumps are "bench rated" by the manufacturer with no loads. In real life conditions a bilge pump output averages just about 30% of its rated capacity; the rest is taken up by heat, electrical inefficiencies and the load of pushing water to and up the discharge port overboard. A good 500GPH pump may only discharge 150GPH on a good day. Hope this info serves as a starting point to bilge info and management.