In one sentence, describe what the following article is about:

When you whistle with your fingers, you use them to hold your lips in place to make it possible to produce the clearest note you can. Every person should decide which fingers to use to create the best possible whistle. Your individual finger positioning will be determined by the size and shape of your fingers and mouth. Consider the following possibilities:  Using both your right and left index fingers. Using both your right and left middle fingers. Using your right and left pinkie fingers. Using the thumb and middle or index finger of the one hand. Whichever combination of fingers you're using, put them together to make an upside-down "v" shape. The bottom of the "v" is where your fingers connect with your mouth. Be sure to wash your hands before you put your fingers in your mouth The two fingers should meet just under your tongue, behind your back teeth. There should be a small hole right between your fingers. Close your mouth tight over your fingers to ensure air only goes through the hole between your two fingers for a more concentrated sound. This technique should produce a loud, shrill sound perfect for calling your dog home or getting your friends' attention. Keep practicing until your fingers, tongue and lips are in the correct position to produce a strong sound.  Don't blow too hard at first. Gradually increase the strength of the air you blow until you make the right sound. Try different finger combinations. You might not be able to whistle over certain fingers but other fingers might just be the right size to produce a sound.

Summary:
Decide which fingers to use. Make an inverted "v" shape with your fingers. Place the tip of the "v" shape under your tongue. Close your lips over your fingers. Blow through the hole.