There are many different types of electric guitars.  The major difference between electric and acoustic guitars is that electrics don't make much sound on their own.  In order to make a lot of sound electric guitars must be plugged into an amp.  They can also have certain amounts of feedback, or distortion that make it sound different.  They're normally made out of wood, but can be made out of metal and/or plastic.  All of them have electric circuits and pickups to pick up the string vibration and amplify the sound.  They are normally used in rock and blues, but can also be used in country and virtually any type of music.  

Acoustic guitars are normally made out of wood, but they can be made out of plastic, metal, and lots of other materials.  Most of them have no electrical circuits or pickups, and can not be amplified.  But, there are some that are built like electrics but can be plugged into an amplifier in order to amplify the sound.  That way you can play for a concert or a big audience or if you just don't feel like strumming it very hard.  The normal acoustic electric guitars are louder than the un amplified electric because there is a special place for the sound to resonate and get louder.  The strings on acoustic are normally much thicker thatn the strings on an electric, therefore, most people think that they're much harder to play than an electric because you have to push down on the strings harder in order to get the right sound.  They're normally use in country, but are used in pretty much everything the electric guitars are used in.

unlike nromal electric and acoustic guitars, which have six strings, basses only have four or five.  Most are electric, but some are acoustic.  They also have a much deeper sound than other guitars.  Thats why they're called bass.