The mouse buttons have two different control modes, Standard and Zoom. You use this option to toggle between them. In Standard mode, the left mouse button is used to rotate about the current focus point. This focus point is always located at the centre of the screen, and is marked by a red transparent sphere during panning and zooming operations. The right mouse button pans the model in the current viewing plane. The scroll wheel is used to zoom in and out on the current focus point. In Zoom mode, pressing the left mouse button zooms in at the current cursor position, and pressing the right mouse button zooms out at the current cursor position. Pressing and holding the left mouse button allows you to drag the cursor over an area which you wish to zoom.
