Archery is a sport that involves some specialized equipment, some of which periodically needs replacement. Maintenance of one's gear is an important part of the game. One such piece of equipment is the string.
It's highly unlikely that one would ever need to shorten a bow string by more than a fraction of an inch; the string is usually sized to the bow, and replacements are not difficult to acquire in the correct size. But some adjustments can be made in order to fine-tune the equipment. Note: This article does not cover compound bows, which require a lot of expensive equipment in order to adjust or replace the string.
String the bow
Using the bow-stringer, put the string in place on the bow according to the instructions that came with the stringer.
With the string on the bow, use the bow square or ruler to measure the distance from the string to the hand-rest. For most adult recurve bows, this distance should be between 8 and 10 inches.
If the string height is too low, you can adjust it somewhat. Unstring the bow, sliding the upper loop down on the limb.
Slip the bottom loop off the lower limb. Look at the string, and you will see that the strands may be somewhat twisted one way or the other.
To increase the string height (distance from the bow to the string), you need to shorten the string. Hold the string between thumb and forefinger, just above the bottom loop. Spin the string between the thumb and finger so that you add twists to it. The more you twist the string, the shorter it gets.