As a fan of agile development, where everything should be structured into small classes, its hard to see regions as anything but a bad solution for a bad problem. But they are here, and people are using them, so no sense in not knowing what they do. Its a simple answer:
They do nothing, zip, nada. A region is simply a construct to enable Visual Studio.NET to hide pieces of code outside of the normal bounderies of methods, structures and classes.
In vb.net a region have the following for:
' types of service:
And in c#:
// types of service:
So no magic here... Sorry