how to execute a process when a file is uploaded

Let me begin by informing you guys about what am trying to do.
I am building an ASP.NET application that takes in an xml file uploaded from the client, and process its information and shows it in an excel sheet on a web page. The process works when i choose a local xml file while testing it in my web server.

The problem is that I do not know how to initiate the process right after the file has been uploaded 100%.

How can I tell the ASP page that when a file is uploaded.... to store the name of the file in memory, so that when its 100% finish it can point to that file and execute the process.

Thanks guys...hope you can help me

Is the process that needs to be executed external (outside the application) or internal?

Internal