This means you need to compute three surface integrals, always using the outward pointing normal vectors. I've included them in the graphics.
Click on the picture below to begin. You can rotate the object by clicking and dragging your mouse. You can zoom in and out if you click, hold down the shift key, and move the mouse up and down. (In some browsers it's a bit different; hold the shift key down, click the mouse button, and then move the mouse.)