Player 1 uses keys from the left-hand-side of the keyboard, while player 2 uses the numeric keypad. The following keys are used to control the meatlings in "Keyboard" mode:
For example, to turn meatling 1 clockwise, press the "D" key and hold it down while the meatling turns until it is facing in the desired direction. To stop the meatling, release the "D" key. In "Cyborg" mode, only the keys which control walking and turning the torso are active (which makes life a lot easier when learning to play).
Players can change which keys control which actions by selecting "Change Controls" from the "Game" menu.
To change a key, select the old letter by clicking on it with the mouse. Then press the new key on the keyboard. The letter should change in the dialog.