In (classic ;-)) ASP.NET 1.1 you had to reference a user control in every page you wanted to use the control in (@Page-directive).
ASP.NET 2.0 lightens this work because it allows you to reference heavily used user controls globally in the web.config file.
When you have added something like this to your web.config:
your user control is avaible in every page of your web project accessing it via
And you have full intellisense support for your user control, of course.