Basics of UG

Mouse Controls:

Rotate:
> Press and hold the middle mouse button (or scroll button) and drag around the screen to view the model in the direction you want. The model can also be rotated about a single axis. To rotate about the axis horizontal to the screen, place the mouse pointer near the right edge of the graphic screen and rotate. Similarly, for the vertical axis and the axis perpendicular to the screen, click at the bottom edge and top edge of the screen respectively and rotate.
>If you keep pressing the MB2 at the same position for a couple of seconds, it will fix the point of rotation (a green + symbol appears) and you can drag around the object to view

Pan:

> Press and hold both the middle button and right mouse button simultaneously and drag OR

> Press and hold <Shift> button on the keyboard and press and drag the middle mouse button. 

Zoom In /Out:

> Press and hold both the left mouse button and middle button (or scroll button) simultaneously and drag OR > Press and hold <Ctrl> button on the keyboard and then press and drag the middle mouse button. OR
> Scroll up and down if the mouse has a scroll wheel

In short form:     

•  Zoom – Ctrl + MB2
•  Pan- Shift + MB2
•  Rotate – MB2

•  MB1 = Left button – Used for selection
•  MB2 = Center button - Acceptance
•  MB3 = Right button – Context sensitive menu