I want to add the custom configsection in the app.config file as follows
I base all my configuration management code on the classes I collected here. This is an example, and here's some documentation. Note that this is code I personally refactored from a blog post that isn't available on-line any more.
You should check out Jon Rista's three-part series on .NET 2.0 configuration up on CodeProject.
Highly recommended, well written and extremely helpful! I've learned how to deal with custom config sections from those excellent articles.
This will help you http://msdn.microsoft.com/en-us/library/2tw134k3(v=vs.80).aspx