The triangle is the used for either incident or reflected readings. Match the numbers from the scale on top where the needle moves to the triangle. The circles are used only if you use the spot meter attachment (sold as an extra device), red being for the 15 degree setting, green is for the 7.5 degree setting. You will use those only if you are using the attachment though, without that, they are simply Christmas colors...
The two scales on top change sensitivities from low light to bright light based on which side of the double switch you push. If the needle does not register or pins on the side, you need to switch scales by pushing the rocker switch on the right side the other direction. The little red box on the scale is for your battery check. Slide the slider switch on the back to the right and the needle should move to that box. If it doesn't, replace the battery. Clean the contacts for the battery every time you change the battery though.
This meter adapts very well to the Zone System scale as well.