Difference Between Aspx And Asp

I understand how asp scripting works and how you put <% %> around your server script. However this is .asp . what is .aspx? is this the new version ASP.nET? I dont understand how it works when i create a new aspx project in vstudio.net and i create a aspx page in design view.

I add a button and then double click it to add code to that button. I dont see any html code around it? In an asp page the server side code is surrounded by html code. An aspx page almost looks like a normal vb application, why is there no html
code around?