The controls of the window are:
Material Icon Array: Shows the material files of the selected folder. You can perform the following actions with it:
Double clicking a preview icon on the material browse window inserts it in the current library.
Drag and dropping a material icon from the browse window into the select window loads the material.
Drag and dropping a material icon to a view window loads the material and maps it to the selected geometric objects (just like drag and drop from the select window's material tab to a view window).
Drag and dropping a material from the select window to the icon array area saves the material to a disk file using material's name as the file name.