APP request: Drink counter

Lame question as I don't get the concept of the display buffer.
I cuccently do

	g.setBgColor(g.theme.bg).setColor(g.them­e.bg).fillRect(0,145,176,176); //Clear
	g.setFont("Vector",20).setColor(g.theme.­fg);
	g.drawString(drinks[activeDrink], (40 * (activeDrink + 1)) -20, 165);

But having this fillRect to clear the previous written number feels totally wrong. What is the right way to do it?