Declaring

Typically collections are declared as module or global variables.
Always put the declaration on one line and the assignment on a different line.

Dim myCollection As Collection 
Set myCollection = New Collection 

Using the Set keyword allows you to create the collection exactly when you need it.
It allows you to test if the collection is Nothing.

If (myCollection Is Nothing) Then 
End If 

Passing Collections In

Passing Collections Out

You must use the Set keyword if you want to return a collection from a function.

Public Sub Testing() 
   Dim myCollection As Collection 
   Set myCollection = MyFunction 
   Debug.Print myCollection.Count 
End Sub 

Public Function MyFunction() As Collection 
Dim myCol As Collection 
   Set myCol = New Collection 
   myCol.Add("mon") 
   myCol.Add("tue") 
   myCol.Add("wed") 

   Set MyFunction = myCol 
End Sub