Hi Rayain,
Assuming you are doing .Net add a reference to the DLL and Create DLL Form
using the proper constructor.
If you need tips on how to start, create a solution with a Windows
Application project and Class Library project (they don't have to be in the
same solution if you are using VS Express). In your library project add a
WinForm class and create the necessary constructor overloads and properties.
In your Windows Application project add a reference to your class library.
In your main form create an instance of the class library WinForm and display
it using Show() or ShowDialog().
If you need further details, please feel free to ask.