W/A/S/D -- move around
Arrow keys -- move around
Ctrl -- fire
weapon
Y -- invert the Y-axis for mouselook
Move mouse -- look around
Left mouse button -- fire
weapon
Right/Middle mouse button -- jump
Gameplay
To play the game, you run around the level and shoot at the targets. Clearly, the game is not much fun at this stage since the targets never disappear (which means you can stand there and rack up infinite points). The main purpose of this stage is to give you the game's source code. Once you have looked through the source code and tinkered around with it, you will be better prepared to modify the game for a project.
You can also do many useful things in the console window (brought down with the '~' key). For example, here's how to change the resolution:
screenwidth 1024
screenheight
768
restartrender
Consult the LTDS docs for other useful console commands.