Verified answer

It goes inside the spring.

The two hooks, hook in near one end, and the flat end slides in near the other end of the spring.

Then simply use a socket and ratchet to screw the two ends closer together.

If you would like to send me you email address I will draw you a diag on how to set them up.

You have to be very careful with spring compressors that they are fitted correctly and that both sides atr taken up evenly and released the same way.

Take it back and get a refund before you hurt yourself. A compressed spring can Kill or maim you if not done right. They are easy to use and easy to get wrong. That is stored up energy there.