This is the part of the guitar that you use to tune the strings and hold them in place. The word "stock" means the part of something that moves. The head just means the top of the instrument
The neck of the guitar is also called the fretboard. It's because the frets (metal slivers glued to the neck) are on the neck.
On the electric guitar (pictured) the body has a few parts.
This is called a "pickup" because it picks up the sound. These are on all electric guitars.
The part of the guitar that holds the strings in place. The bridge can be used to raise or lower the strings from the fretboard.
The knobs control the volume of the guitar and the tone of it as well. The pickup selector is used to change which pickup is used. The different pickup locations change the sound of the pickup.