Unexplained Compiler Error Writing A Function

I keep getting Expected: = when trying to write a new Function in a module in my Access Database. Can't understand it.

Even some code as simple as follows causes this.

Function OpenInterface()
Dim variable As String
Set variable = "help"
Debug.Print(variable)
End Function

It doesn't cause error if I include an argument, though I want to to create 2 tables from some existing tables, but not to return anything and there are no arguments. Should I be using a Sub? In which case... can someone help out in how I go about writing the opening and close lines.