There are three main factors on how the sound of the guitar is produced. First is the strings. The strings when plucked or strummed vibrate but the string itself does not produce a loud sound when it vibrates. This comes to the second factor - the body of the guitar helps.
When the strings are attached to the body, it creates more vibration as the air from the strings being strummed bounce back from a solid body. Third, is the way you will play it either by plucking the strings or strumming them. Plucking a string produces a more solid sound of each note while by strumming you make all the strings sound.
In all guitars, the sound is produced by the vibration of the strings. However, because the strings can only derive a small amount of air, the magnitude of the music needs to be elevated to be heard. In an acoustic guitar, this is conducted by using a soundboard and a resonant cavity, the sound box.
When the string of the guitar vibrates, the faster the vibration, the higher the pitch of the note. The entire top of the guitar echoing is what causes sound waves. Guitars with holes that are not on top are often louder because the lack of the aperture means more air mass can be moved.
