I tried to follow the old adage "expose for the shadows, develop for the highlights", so that I can capture the shadow detail.
I only have Nikon FM2 light meter. How can I meter the shadow with it?
In contradiction to (handheld) spot meters and incident light meters, reflective light meters such as the one in your FM2 are harder to use for precise metering.
As explained in this answer, spot meters have a very narrow angle of view, thereby metering only a small part of the entire scene. With such specific metering, you can imagine it is not all too difficult to meter for the shadows: point your meter at a general shadow and you will have a reading for the shadows.
With incident light meters, which are usually handheld meters, metering for the shadows also isn't much of a task. Hold the white lumisphere so that it is pointed at the light source but is entirely in the shadow, and you'll have a reading for the shadows.
Now, trickier is to meter with a reflective meter.
Reflective meters have a fairly large angle of view. That's also why it can be fooled by points of light as with your previous question.
What you could do, is a bit dependant on the situation. For starters, determine how the light is spread on the scene and how this affects your light meter. If your light meter is centre weighed, and there is a good amount of shadow in the centre, leave the light meter to do its job. If the opposite is true, there is one of two things you can do:
1) Use the exposure compensation dial. This dial usually ranges from -3 to +3 stops. How far you will have to turn this dial depends on the contrast between the sunlight and the shadows. If the sun is very bright but the shadows very dark, then this can differ quite a few stops, but a good starting point is +1. You add stops because your light meter will expose for bright sunlight, thereby underexposing the shadows.
2) Shift your camera to a more shadowy area, and take a reading off of that. Some cameras feature a exposure memory button that allows you to do this easily, otherwise you will have to either manually set the exposure or use the aforementioned exposure compensation dial. This shadowy area has to have a similar 'brightness' as the shadows in the scene you want to photograph. Let's say your meter reads 1/500 at f4 on your scene. You turn the camera to shadows and read 1/125 at f4. If you have an exposure memory button, you hold this and take the shot. If you don't, you either manually set the shutter speed and take the shot, or you use the exposure compensation dial and set it to +2 (as 1/125 is two stops more than 1/500).
Also, remember that flipping your camera to take a vertical photo also flips your light meter. If said meter is bottom weighed, than it will now meter the left or right of the scene, depending on how you turned the camera!