There are three things you must do before it will work correctly.

First make sure there's a battery in it. ;-)
The battery compartment is at the front. The smaller button on the front is
the compartment door catch.

You can test if the battery is still good by pressing the large button on
the meter prism's front for 1 second.
A green light will appear in the window above the letters BAT on the prism's
right rear.

Second, set the correct film speed.
You do that using the front of the two small levers in the circle on the
meter's left side. The values appear in the window on the meter's left rear.
Set it so the correct value appears between the two lines.

Third, you must set the maximum aperture of the lens you have on camera when
metering. You have to change that every time you change lens.
You do that by using the rear of the two levers in the circle on the meter's
left side. Again, the values appear in the window (marked MAX) on the
meter's left rear. Set it so the correct value appears between the two
lines. If the aperture of the lens currently on the camera isn;t on the
scale, just set the thing so that the two adjacent values appear on the
lines in the window, i.e. such the missing correct value would appear
between the two lines.

To meter, you must make sure the aperture in the lens is not closed (which
it would be if you are using the DOF preview lever).
Then it's a simple matter of pointing the thing so what you want to meter
appears in the center of the image (the meter is center weighed, so it's
important to aim it correctly), and then press the large button on the front
for at least 1 second again.

The display will show the EV-value to use. You have to set the aperture and
shutterspeed on the lens accordingly yourself.
If two numbers light up simultaneously, the correct half-stop EV value to
set is the one in between the two lit.

The meter will switch off automatically after about 20 seconds. You'll know
because the display leds will be off.

Don't know.