The acoustic guitar sounds amazing by itself, there's no question about it. Still, as a guitarist you'll almost certainly run into situations where the instrument could use a helping hand. Whether that's to gain extra volume for filling the room at a large venue or simply to be heard better over the other members of a band, an acoustic amplifier will give your guitar the boost it needs to deliver more power than the acoustic sound box alone. Since acoustic guitars have such a distinctive sound, the goal of any amplifier built for them is accuracy. You may be using a plain acoustic guitar with pickups attached or an acoustic-electric with the pickups built in—either way, these amps are designed to reproduce the sound as closely as possible. With that said, most acoustic guitar amps do also come with a range of built-in effects: in many cases, enough to go toe-to-toe with an electric guitar amplifier. By giving you these options as well as the ability to connect effects pedals and stompboxes, an amp can serve as a bridge between your acoustic guitar's sound and an electric guitar's versatility.
As with electric, there are two main configurations for you to choose from when it comes to acoustic guitar amplifiers: either a combo amp or an amplifier head and speaker cabinet. Each setup has its own advantages. For a combo amp, the benefit is portability. These amplifiers pack all of their components into one box, making your pre-show setup as easy as setting the amp onstage and plugging it in. The two-part setup, on the other hand, is good for high-power use and adaptability. An amplifier head can plug in not only to a speaker cabinet, but also to a mixer or directly to a venue's own loudspeakers—and while combo amps are powerful enough for most stages, if an outdoor show or a huge venue demands truly awesome volume, a beefy cabinet paired to an amplifier head will deliver.
The bottom line is this: when you need to make yourself heard, an amplifier for your acoustic guitar will get the job done. Decide whether you need a combo amp or a two-piece head and cabinet system, pick out a model with the power level and effects selection that fit your usual venues and styles, and take home the amp that's right for you.