VBA : How to change the cell's value in a function?

I'm a new vba programmer and I have some trouble.

This is my function :

Function CopiePaste(CASEREF As Range, REF)

Dim o As Range

For Each o In CASEREF

   o.Value = REF

Next

End Function

I want define multiple cell's value in a function but my code doesn't work and I don't understand why ?

Thanks in advance