Begin by clicking on one of the buttons on the left of the applet to draw a rectangle of the listed dimensions. Then respond to the questions the applet asks. When prompted for the area click your mouse in the bottom text box, then type the area in numbers and click the enter button on the applet. When prompted for the formula for the area use the abbreviations for length(l), width(w), or perhaps side(s). Use the * to represent multiplication. For more on computer mathematics see this page.