Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
This wiki article seems quite helpful:
http://en.wikipedia.org/wiki/Random_walk#Random_walk_on_graphs
EDIT If you don't like the wikipedia, see http://www.fis.unipr.it/stat/PAPERS/PRStPh0027.pdf
