Once the room has loaded, press the spacebar. The text in the box below the Action window will switch from Interactive Mode to Movement Mode. Then...
In order to move forward/back, move the mouse forward/backward.
In order to turn left/right, Move the mouse left/right
In order to Stop, Click the right mouse button
In order to slide left/right, hold down the left mouse button, slide left/right
In order to tilt view up/down, press up/down arrow
in order to raise/lower height, press left shift/ctrl
in order to run (move fasster) Press R when moving.
If you don't have a manual for the game, you should be able to download one if you bought the game from GOG.