No, not being thick
- you are spot on. The histogram is much like any other graph - an x axis on the bottom and a y axis top to bottom. As relates to photography, the x axis goes from 0 - 250 with zero being complete black and 250 being white. Distribution is shown on the y axis.
So yes, the histogram is to be used as a guide - if the subject matter is predominantly dark then the histogram will be more to the left. It's up to you as the photographer to judge the histogram as it relates to the subject matter.
With your never ending thirst for knowledge
here's an excellent tutorial site - and yes, histograms (in detail) are explained. Enjoy.
http://www.cambridgeincolour.com/tutorials.htm