In the NodeXLApi.chm help file included in the NodeXL Class Libraries download, there are complete, compilable source code samples for getting started with using the NodeXLControl in your application. See the NodeXLControl Class topic.
Are you more familiar with Visual Basic .NET? The NodeXLControl can be used with Visual Basic .NET; you are not required to use C#.
If you want your program to do something when the user clicks a vertex in the graph, your program can handle the NodeXLControl.VertexClick event. The event arguments include the vertex that was clicked, so you can tailor your handler’s code for
specific vertices. See the NodeXLControl.VertexClick Event topic in the help file for details.
If you have a more specific question, let me know.