Here is a diagram of an acoustic guitar.
I'm proud to say that I built the guitar pictured in the diagram.
Below the diagram of an acoustic guitar you'll find explanations of the acoustic guitar's parts and their function.
The parts labeled in red are must know and the ones named in black you should know.
Body: The body of an acoustic guitar is the large section of the guitar below the neck. The body amplifies the vibration of the strings when a note or chord is played. Different woods provide different tonal qualities and effect the "voice" of the guitar. Plywood does not vibrate as freely as solid wood, and the glue used in plywood does not transmit vibrations at all, which makes the tone thinner sounding.
Bridge: The bridge attaches to the body and the strings get pinned into the bridge. The bridge is very important to the tone and plastic bridges are horrendous at transmitting sound. Once again the type of wood used here influences the voice of a guitar.
Bridge pins: Bridge pins are used to hold the strings in the bridge.
Frets: The pitch of a note is caused by the frequency of the strings vibration. When the string length is shortened by being pressed against a fret it's frequency gets higher and so does the pitch of the note.
Headstock or Peg-head: The part of the neck above the nut where the machine heads are attached. The headstock affects the volume and sustain a bit. Larger headstocks absorb more string vibration than smaller peg-heads.
Machine Heads: Machine heads are sometimes called tuning knobs or tuning buttons. They tighten or loosen the strings. Cheap machine heads can be difficult to turn or loosen the string tension quickly, or worse yet keep breaking strings because of sharp edges.
Neck: The neck is the long part from the body up.
Nut: The nut is the piece of material between the fretboard and the headstock which the strings rest on.
Saddle: The saddle is the part that fits into the bridge that the strings rest across.
Soundboard: The soundboard, (also called a top), is the face of the body. This is where most of the sound is produced. A quality solid wood top is very important to the guitar's voice.
Sound hole: Contrary to popular belief the sound hole does not allow the sound to escape out of a guitar. It's size actually affects the balance of treble and bass tones.
More Resources ...
You will also find a diagram of the interior of an acoustic guitar, and descriptions of the various parts here:
Inside an Acoustic Guitar Diagram ... How Construction Affects Tone and Quality
Not all acoustic guitars are created equally. There are huge differences in prices and sound quality of acoustic guitars, including construction methods and the types of woods used to affect the sound and playing ease.
For in-depth information about types of acoustic guitars, acoustic guitar construction, and tips to help you find the best guitar for you visit:
Types of Acoustic Guitars and Guitar Buying Tips.