*.vbs > how to declare dll in visual basic script???

I try to write a .vbs file which contain some function.
But i need to refer to some dll/component.
In VB, i can click "Project>Reference>....." but in vbs i cant to like that?
Another problems is how to declare function in .vbs file?
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Public Function Main()
Some coding here...
End Function
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Any ideas would be very appreciate!