visual studio 2010 - IIS 7 ASP.Net 4 - Code Behind Auto Compile Not Working -

I removed my first asp net 4 app together with Visual Studio 2010 and IIS to compile my code It does not seem to be flying behind for some reasons, I have to build this site manually

How can I configure my app to compile the rear code on the fly? I looked around but I should remember something.

BD

Now type two web site types < The code should be compiled before the code, the web application and the web site , the latter can be compiled on the fly.

You create a file> new> project ... from web application ... you create from web site site> new> web site ...