The csc.exe command invokes the compiler on our source file, asking it to produce a Windows application via the /t flag (where the "t" stands for "target"), pulling in the System.Windows.Forms.dll library using the /r flag (where the "r" stands for "reference"). The job of the compiler is to pull together the various source code files into a .NET assembly. An assembly is a collection of .NET types, code, or resources (or all three). An assembly can be either an application, in which case it has an .exe extension, or a library, in which case it has a .dll extension. The only real difference between the types of assemblies is whether the assembly has an entry point that can be called by Windows when the assembly is launched (.exe files do, and .dll files do not). Now that that the compiler has produced MyFirstApp.exe, you can execute it and see an application so boring, it's not even worth a screen shot. When you close the form, MyFirstApp.exe will exit, ending your first WinForms experience. To spice things up a bit, we can set a property on our new form before showing it: