ok so it looks like you forgot the color code wether its a preset or RGB lets say gfill, its set like this gfill x[start],y[start,x[finish],y[finish] color. so for a small box try, "gfill 0,0,50,50,RGB[20,120,255] "
you should now have a small blue box in the left hand upper corner. mess with each number one at a time to see the effect, all "g" codes work this way, exsept gcercal witch has one less input, hopes this helps to get started