Pass sub variable to function

Hi and thanks in advance for any help.

How can I pass a variable from a sub to a function? My codes are below:

Sub Main()
Dim Source, Dest
Source = Z24
Dest = T28
SpecialFunc
bla, bla, bla....
End Sub

Function SpecialFunc()
Range(Source).Select
bla, bla, bla....
End Function