I am creating game like bow and arrow. I want my hero will shoot the arrow with the strength meter, how will create the power?
The meter is simply a visual indicator of the amount of force that will be applied to the arrow when the bow is released. How you display that number is going to be specific to the style of your game and what you're using for the GUI.
Choosing the amount of force will also be dependent on how you want the game to work. A simple method would be to slowly increase a value to the maximum amount, as long as the user holds the fire key. When the fire key is released, the value generated is used and applied to the arrow as a force in the direction the arrow is pointing.