working with C#.net 2008 solution

I am basically new to C#.net 2008 working with the professional version. I have a solution to work with that has lots of projects in it with no documentation. I need to determine how this solution works. I know I would look in the properties to see what the startup project is. However after that, I was wondering if you have any suggestions on how to determine how this application works in addition to stepping through code.
  Can you tell me how I should go about determing how this application works.