There are two groups of radio buttons and a reset button. The choices in the first group consist of transformations, setting the pivot point and setting the transparency color. The second group allows you to pick between the two environment modes, GL_REPLACE and GL_DECAL. You should have experimented with the two modes in the tutorial Texture Coordinates and observed their respective effect on the rendered texture map.
Recall that when the mode is set to GL_DECAL, the alpha (transparency) value of the border color and the texels is applied. As seen in Texture Coordinates, when the alpha value of the border color is set to zero, the border color is fully transparent and the underlying color of the geometry appears. The same can be said when the alpha value of a texel is set to zero.
A parameter input dialogue appears based on your choice made in the selection panel. In the case of setting the transparency color, five changable parameters appear. The first three are the rgb values of the texel color we want to make transparent or at least change its alpha value. The fourth is the alpha value and the fifth is a tolerance. The tolerance is for establishing a range of texel colors near the rgb color we set. The alpha value of those texels will also be changed.
The controls for changing parameters are the same as for the parameter input windows in other tutorials.