How does TileImage work?

TileImage parameters are image:TImage, x# = 0#, y# = 0#, frame = 0 but I don't now what x and y exactly are. I've tried TileImage dotImage, 640, 480 (the resolution of the screen) and TileImage dotImage, 100, 100 (the width and height of the image) but whit no luck.

Thanks anyway, Nicolas.