The guitar head is like a real head. Without it, your guitar is basically useless and unplayable.
The Head Stock
The head stock of the guitar is (depending on the guitar) usually a rectangular piece that holds your tuning keys. Here, the strings of your guitar wind around the pegheads. These keep your strings tight and in place, so that when you move the pegheads, tuning is possible. Without the head, your guitar is basically useless. The head is also the most abused part of a guitar.
Tuning keys. A vital component of your guitar. If damaged or used improperly, the guitar will not be tuned, and your playing will suffer.