I assume you mean that the bilge PUMP is not working? The bilge is just the lowest part of a boat - in your case, under the engine. The bilge pump is in the bilge. Check battery connections, fuses, dash switches, etc. - looking for power at the switch, leaving the switch and at the pump. Operate the float switch by hand and see if the pump comes on. The results of these things will get you headed in the right direction to fix it.
It's probably under the engine. It should snap off the housing so you can pull it out to get at it. Bring a meter with you and check all power connections. The pumps themselves rarely go bad unless they get jammed or run dry. The float switches tend to fail. Good luck.
