The Pan tool allows you to move/scroll the mat. You can also use the vertical and horizontal scrolls bars around the mat.
To use the Pan tool, first select the Pan tool from the Tools panel
If you are using the Selection tool
, you can hold down the Space bar on the keyboard to temporarily switch to the Pan tool and drag around while the Space bar is held down.
Click and drag to move/scroll the mat.
Example of moving the mat around using the pan tool.