X, Y, Z Axis checkboxes
The values in these boxes define the range of the transition. Between the values, the shader will run from 0 to 1. Outside the values, the shader will be 1 or 0.
Greater and Lesser radio buttons
This setting determines where the shader will go to zero. If it is set to Greater, then any coordinate larger than the largest value in the Range boxes will return a 0.
And and Or Mode radio buttons
These buttons determine how the cuts on the various axes are combined. In AND mode, in order for a point to return a 1, all three axis controls must individually return a 1. In OR mode, only a single axis control need return a 1 in order for the whole shader to return a 1.
Global and Local radio buttons
Use randomize shader checkbox
Sets the strength of the random effect. Large numbers make it more difficult for the value to get to white.