An assembly is a .NET executable, i.e. DLL or EXE. Read the documentation for the types you want to use and you'll see what assembly they are declared in. If your project doesn't have a reference to that assembly, add one. Importing a namespace is useless if your project doesn't know that types in that namespace exist. You should read this:

http://jmcilhinney.blogspot.com/2009...importing.html