In the Chess GYM you can sharpen your chess skills, try chess openings you learned in the opening section, or just have some fun. You can play against a computer program which is about 1800 ELO or challenge online opponent. Don't get upset if you loose. It just means you need to study more chess. Remember we learn the most from the games we loose, don't forget to go over your game later on. Good luck!
If you feel you need stronger oppenent, check out our ChessEngines section where you can find top rated chess programs like Rybka and TogaII.