(line x1 y1 x2 y2)
Draws a line (a direct path between two points) to the screen. x1, y1, x2 and y3 are all numbers which are being used as coordinates, or pixels from the top left on your screen.
(rect x y width height)
Draws a rectangle to the screen. x and y are coordinates. Width and height are how big the box is, again in numbers.