The Action Buttons appear in the tool bar along the top of the screen. Generally, they are used to quickly and interactively move the overlay image into position. Most of the buttons auto-repeat, so if you hold them down, you can quickly pan or zoom the the image.
You can also do this by directly dragging the image and the frame around the image with the mouse. This is usually quicker and more intuitive than using the buttons.
However, the buttons can be used to do very small increments that are difficult to do by hand.