How about googling +Dijkstra +c# +"shortest path" - yields a good hit:
http://cs.nerdbank.net/blogs/jmpinli..._CallBack=true
(I cannot vouch for the quality of code / math)
However; graph theory is by definition quite math orientated; if you don't
understand the math, I would advise sticking to pre-written code - otherwise
you will struggle to maintain it. Or - go to the library and get a book on
graph theory; some books make it quite easy to follow with visualisations
etc - note that "quite easy" in this context is subjective.
Marc