Acoustic guitars come in all shapes and sizes and they range from a wide variety of prices and costs. The standard acoustic guitar will cost you about $500 and will only feature six strings. Although these are commonly used the most there are still fairly other popular models of acoustic guitars.
The 12 string acoustic guitar is another popular type of guitar because it produces a sound that is far richer then a 6 string guitar. Beginners will find a 12 string a lot easier to play as well since it is generally easier to fret the notes. The only major difference between the two is that you play twelve strings instead of just six.
If you are unsure as to what type of guitar you want to buy, then I would recommend that you get a standard six string and then after if you like, you can try using a twelve string. I say this because most pop and rock songs will use a six string because it is far more common sounding then other types of guitars.
Generally a twelve string guitar is used in classical or very strong acoustic pieces. If this is the style of music that you play or that you like then you may want to get one for yourself. Usually the price for a twelve string guitar is slightly more than others.
The best thing you can do is to go around on other websites and look at reviews and see what types of guitars get the most positive feedback. You can then decide what type of guitar is right for you.