Find a shader from the game that does what you want, for example the scrolling starfield, or a custom shader that does that like the coruscant ads, and look at the shader code. THe thing that makes it scroll is "tcmod scroll x y" where x is the speed for x scrolling and y is the vertical component. Cannibalize from other shaders like I do, you'll learn fast from that
There's always the shader manual from the editing tools, too.