In acoustic guitars sound is achieved by the strings vibrating over a large hole and resonating outward. Most acoustic guitars are made of "tone woods" like spruce or cedar, which are known for their ability to circulate air and resonate sound. Body shape and size are dependent on manufacturer and model. Some acoustic guitars nowadays are even made with different materials such as carbon fiber.
Electric guitars are most commonly solid body or semi-hollow depending on the style of music and the type of sound the player is trying to achieve. Bodies once again come in many different shapes and sizes according to manufacturer and model of the guitar.
Unlike acoustic guitars electric guitars don't produce sound through the use of a hole in the body. Electric guitars rely on pickups and amplifiers to produce sound. Pickups are transducers placed on the guitar that "pick up" string vibrations and convert it to electrical energy. Once this energy is amplified, a sound is produced through whatever is being used to amplify it. Pick ups generally come in two shapes. The humbucker, and the single coil. (pictures will be shown near text.)
Certain pickups are known as "active" pickups, meaning that an extra power source, usually a 9 volt battery, is placed inside the guitar to even further amplify the sound giving it a much brighter and sometimes aggressive tone.