Here is a walkthrough, Using PostgreSQL in your C# (.NET) application (An introduction):
In this article, I would like to show you the basics of using a PostgreSQL database in your .NET application. The reason why I'm doing this is the lack of PostgreSQL articles on CodeProject despite the fact that it is a very good RDBMS. I have used PostgreSQL back in the days when PHP was my main programming language, and I thought.... well, why not use it in my C# application.
Other than that you will need to give us some specific problems that you are having so that we can help diagnose the problem.