Tips on how to Win: The Knights have a stamina system just like yours in the game. If you wait for them to lose their energy, you can attack them more easilly. Your shield is the best defense, use it often. The special attack key is only useful if you acquire the specific upgrade, using it otherwise will just waste energy.
The Boss is the Grand Master Teutonic Knight, once he's dead, you have to finish him by pressing the Down key, on his corpose.
Please read the "How To..." page and the other pages, to know how to play.