This is the Argument Editor. The editor is available from the main menu under Render->RenderOptions. It allows you to control which of the unconnected inputs from the all the boxes on the desk, become arguments to the shader. Simply click the button opposite its ShadeTree given name. It is a good idea, but not necessary, to change the name of the argument to something descriptive of its function in the shader. The arguments you select will show up in the SoftImage application.