If you're a new acoustic guitar player, you probably have some accessories that people usually get along with their guitar purchase. One of the most important things you can have is an acoustic guitar tuner. If you're new to the guitar then your ears aren't trained enough to tune an out of tune guitar. You can probably hear that it is out of tune, but don't know if it's sharp or flat. If a pitch is sharp, then it is too high, if a pitch is flat then it is too low. All the strings on your guitar must be right on, neither sharp or flat. If not then your chords will never be in tune.
Typically beginner guitar kits will come with a pitch pipe tuner for acoustic guitar. Again, if you're a beginner you probably can't match pitches well enough to use one. Not to mention the fact that they aren't always that accurate. What you can do is get an electronic tuner for acoustic guitar. I say acoustic guitar, but most of them can be used for electric guitars too. Most all tuners come with a microphone and input jack, so you can tune either an acoustic or electric guitar.
Your standard acoustic guitar tuner will have a needle or electronic representation of a needle. This needle will swing to the left when the pitch is flat and swing to the right when the pitch is sharp. It will point straight up when the pitch is in tune and usually has a little green light to show you that it's in tune. If you're a beginner then you should get a tuner for guitar, these are specifically made for the strings on a guitar E, A, D, G, B and E from low to high. There are chromatic tuners that will tune any note, but those are a little more confusing if you're a beginner.
Acoustic guitar tuners are relatively
inexpensive, you can get them for $20 and under and they're a good
investment. The best acoustic guitar tuner, is really opinion, but
if you want to spend a little more you can get a clip on guitar
tuner. It doesn't have a microphone, it works by clipping onto the
headstock of your guitar. It picks up the vibrations to sense the
note. The benefit is that it works with acoustic guitar tuner and
electric guitar tuner. It also works in loud situations, sometimes
tuners with microphones, pick up extra sound that throws them off. Go ahead and get one, because if you aren't in tune everything else will be wrong. If you'd like to see some acoustic guitar tuner reviews you can see some here.