Unique items in combobox on userform

Yes that's right
I tried to edit it by myself but i'm confused about the parameter in these lines

Private Sub ComboBox1_Click()
    Call cValues(ComboBox1.Value, ComboBox2, 2)
End Sub
Private Sub ComboBox2_Click()
    Call cValues(ComboBox2.Value, ComboBox3, 1)
End Sub

I think it is related to the column number of data i need to populate..but when trying to edit i got errors