How do I read Histogram?

[idmax]

From my understanding of the Histogram, if the mountain are higher in the left, it means it's too dark and to the right, too bright.
So question is, when taking photos, must the peaks be in the middle or spread through out?

And, how do I adjust the peaks to be in the middle?


Thanks....

 

[Revo]

http://www.dpreview.com/learn/Glossary/Digital_Imaging/Histogram_01.htm

http://www.naturephotographers.net/mh1101-1.html