Simply run the game and press SPACE to begin play. Move the Knight around 8-directionally (I made that phrase up) using Q,W,E,A,D,Z,X and C or use Kempston joystick.
The aim of the game is to find the Chalice* and the key to get back into the castle. Return the Chalice to its rightful place in the castle.
*The Chalice in this version is Golden Skull because it was included in the licensed graphics and I just liked it.