The left and right mouse buttons control the molecule on the screen.   

To rotate the molecule around the x-, or y-axes, hold down the LEFT button and drag the arrow across the screen.
 
To rotate the molecule around the z-axis, hold down the LEFT mouse button while holding down the keyboard SHIFT  key and move the arrow horizontally.

To zoom in on the molecule, depress the LEFT button while holding the keyboard SHIFT key down; then drag the mouse arrow upwards or downwards.

To reposition the molecule in the frame, depress the RIGHT  button while holding the keyboard CONTROL key down and drag with the mouse.

To edit the molecule, click on the molecule with the RIGHT  button to reveal a MENU, the main features of which are:

•  SELECT applies to protein structures etc which have been appropriately labelled.
•  RENDER permits alternative display of the molecule, some of the buttons being relevant only to appropriately labelled proteins etc.
•  LABEL permits the addition of atom labels etc.
•  COLOR permits changes to the colour of ther display.
•  ZOOM and SPIN allow the molecule to be zoomed in/out and to be spun.