UV mapping is pretty daunting process at the beginning. Caveat: I haven't really done much UV mapping, this is just the way I understand it.

The basic idea is to flatten out your mesh to a 2D space so that there is a little as possible stretching and skewing. This way you can paint a detailed 2D image, and this will wrap around your 3D model. Of course there will be seams and areas (like curved parts) where it is difficult to achieve a flat representation Think about a map of the world (Canada's bigger than it looks!). This is the challenge of UV mapping, and the reason why you have stretching in your texture.

So, look at the basic tutorial of UV mapping in maya (I think it's a cereal box or something) to get you going. I think unfolding a head mesh will be quite challenging, though necessary for a good texture. Hope that helps. Good luck!