Welcome to the Forum,
The thru-hull near midships and above the waterline may be a sink drain if there is a galley in your boat.
I mean no offense, but.......Perhaps a Coast Guard Auxillary course on Sailing and Seamanship would be a good first step for you. Certainly before launching your new boat learn the basic name and function of its parts, its controls, and safety on the water.
Check the DRmarine site for owners' manuals for Oday boats and specific replacement parts. Although many parts could be generic, D & R Marine has information on the brands used originally.
Best Wishes on learning to safely sail your boat and on enjoying its sailing characteristics.