Set the values you want to apply, then click on Move, Scale or Rotate to transform all picked shells. If no shells are picked, all unlocked flattened shells are modified. If Local is ticked, the scales and rotates will pivot around the center of each individual shell, otherwise the origin (i.e. u=0, v=0) is used. Use the Invert button to invert all values so you can quickly transform shells back to where they were, and the Reset button resets the field values back to their defaults.

The three green buttons to the bottom left represent the left, middle and right mouse buttons. By default these are all on, indicating that you can rotate (left), translate (middle) and scale (right) shells by holding down the Space key. Click on any one of the green buttons to turn that function off. For example, if you don't want to accidentally scale any shells, click the third button so it turns gray.

Rescale U & V 

Use these buttons if you want to rescale shells so that their size in UV matches that in 3D. For example, if you load an OBJ with existing UVs and some shells are red and others are blue, clicking on the & button will rescale each of them up or down until they are closer to green in shading. Click on the U or V buttons if you only want to scale in that direction. As with the other transform buttons above, the rescale will only affect unlocked flattened shells. [Example]