The club hosting the event will provide the map. A compass may not be needed for a beginners' course. If you have one, bring it. Any compass in which you can see the needle will do for now.
Some clubs have compasses to rent.
If you want to buy a compass, a simple orienteering compass, like the one shown below, is available for about ten dollars. The cheapest one is fine, but get one with a clear plastic baseplate meant for orienteering. A lanyard for the compass is helpful. Wear comfortable walking clothing that you don't mind getting a little dirty. If it's warm, wear light pants but not shorts, since you may encounter brushy vegetation if you go off trail.