Scope

By default all functions (and subroutines) are public which means they can be called by code in ANY other code modules.
For clarity it is often good to prefix your function with the word "Public"

Public Function MyFunction() 
End Sub 

Function MyFunction() 
End Sub 

Private functions can only be called from within the SAME module.

Private Function MyFunction() 

End Sub 

Any functions will not appear in the (Tools > Macro > Macros) dialog box.