Electric guitars do not produce any audible sounds, they have electro-magnetic "Pickups" that convert the vibration of the strings into an electrical signal. The electric guitar is plugged into an Amplifier (Amp), which produces sounds from the vibration signal it receives. All electric guitars require an amp or other electric amplification device. Acoustic-electric guitars, however, do make audible sounds - as they are essentially acoustic guitars with a built in pickup microphone. you (or they) can plug an acoustic-electric guitar to an amp to increase the volume, or to use guitar effects with it. Guitar amps are rated in Watts, which is the amount of power they draw. The amount of power is directly proportional to the volume level a guitar amp is capable of; the higher the wattage, the louder the amp. For home use a 10 or 20 Watt amp should be sufficient. Concert halls use multiple 1000+ Watt amps, but they are huge spaces. Guitar amps have a speaker in the casing; and amps with higher power ratings have larger speakers, which increases the overall size of the amp case. you (or him or her) may have noticed huge stacks of speakers behind your favorite rock guitarist (see picture above).