Slide the end of your tube through the tube key's slot until the end of your tube is just passed through.
Wrap your tube around your tube key (like swaddling a baby, or making a burrito) while gently pressing the tube against the sides of the tube key slot until all of the tube's product has been pushed to the tube's opening.
Works like a charm!
Worth getting the main squeeze to access all the serum in the tube. Very efficient and easy to use!