Here’s how…
1. Place a stick upright into the ground.
2. Use a small stone or object to mark the spot on the ground at the tip of the shadow that is cast by the stick.
3. Wait about 15 minutes.
4. Add an second mark at the tip of the shadow cast by the stick in its present location.
5. Place a stick, or visualize a straight line between the two marked spots. This line is your approximate east-west line, the west end being the end where marked the first spot.
Note: The reason to wait at least 15 minutes between the 1st and 2nd mark is to establish an accurate 2nd position of the shadow. Too soon and you may not be so accurate. If you marked properly, you will notice that even if you had waited an hour or more between marks, the east-west line will be the same as only the shadow length changes based on the attitude angle of the sun in the sky with reference to the horizontal.
Source:modernsurvivalblog.com