What a guitar amp does is pretty self-explanitory, it's even in the name. It amplifies the sound of an electric guitar. Although an acoustic and electric guitar operate fundamentally differently, similar principles apply to both, strings vibrate at a specific frequency, the sound waves then resonate though the wood and air, creating sound, however, electric guitars have their own method of amplifying the sound, an amplifier. Electric guitars all feature some kind of pickups, which pick up the sound from the strings, and send it to a quarter inch audio jack on the guitar. That jack, with some assistance from a quarter inch cable, can then in turn be plugged into an amplifier. Many common guitar amps feature both the amplifier as well as a speaker within a single enclosure, however many higher end amplifiers will require a speaker cabinet, as they do not have an integrated speaker. The amplifier itself amplifies the electronic signal, that is picked up by the pickups and transmitted via the quarter inch cable, and then sent to the speaker and played back much louder than the initial sound created by the guitar itself.