Do the following to manipulate the molecules.

Click and hold the left mouse button and move the mouse to rotate a molecule.

Shift + click and hold the left mouse button and move the mouse to zoom in or out.

Click the right mouse button to see the menu.

Shift + click and hold the right mouse button and move the mouse to rotate in the plane of the screen.

Ctrl + click and hold the right mouse button and move the mouse to move in the plane of the screen.