Press the 'M' key -  this will let you move using the mouse.
Use the left mouse button to shoot.
Pressing 'M' again will return you to keyboard control mode.

Keyboard controls:

'W' OR Up arrow - Move Forward
'S' OR Down arrow  - Move Backward
'A' OR Left arrow - Turn Left
'D' OR Right arrow- Turn Right
'R' - Tilt weapon upwards
'F' - Tilt weapon downwards
Left Mouse Button - Shoot
Design credits belong to IDSoftware, creators of the legendary game Quake3.
If you want to create a game yourself please visit Morfit 
Have Fun!
The Morfit Team