Electric guitars have pick-ups (a type of inbuilt microphone) and need to be played into an amplifier (amp) to be heard.
The solid body electric is commonly used in Metal, Rock, Blues and Pop Music. Famous solid body guitars are the Gibson Les Paul and the Fender Stratocaster.
The hollow body electric (semi acoustic) is most commonly used in Jazz and Blues music.
Acoustic guitars can be amplified by using a microphone placed near the sound hole or by placing a portable pick-up on the body of the guitar e.g. for performances at large venues where the acoustic guitar needs amplification to be heard.