The 'using' directive only imports namespaces - it doesn't directly import classes or their members.

If your class library, ClLib.dll, has a namespace called ClLib, then in your Windows app you just want:

using ClLib;

To create an instance of your Express class (assuming it has a constructor which takes no parameters) you can then do:

Express exp = new Express();

I don't know what 1E1 etc are but they're not legal identifiers in C# and so won't compile. A legal identifier must begin with either a letter or an underscore.

Although it's not used very often, there's also a variant of the 'using' directive which enables you to create an alias for a class:

using Exp = ClLib.Express;

We can now use 'Exp' instead of 'Express':

Exp exp = new Exp();

However, there's little point unless you're abbreviating a very long name or want to avoid confusion with a similarly named class in another namespace.