The Mandolin evolved from earlier lute family types of fretted instrument, in Italy during the last century, and reached a peak in popularity around 1895. Most of these examples were made in Naples, and the Neapolitan style mandolin has a deep bowl back constructed from thin ribs of wood.
In the late 19th century, American instrument makers developed the flat backed style of mandolin. Gibson's carved models, and Martin's flat tops are the best known of these. These designs give a more open sound, which projects well, and they also have the advantage of being much more comfortable to hold. Most modern styles of mandolin playing use these flat back instruments.
Mandolins are tuned to G,D,A,E, like a fiddle, with two strings to each note, which helps to give it a really big sound. It's very easy to learn to accompany tunes on the mandolin by learning a few simple chords, but you can also learn to pick out tunes or play more complicated accompaniments