Hook both ends of the ratchet strap to something.
Fold the ratchet as shown in the picture below. Then insert the open end of the other strap “through” the ratchet cylinder.
Pull the open end through the ratchet as far as you can until there’s tension in both straps.
Pull the handle of the ratchet back and forth until straps are tight. You should only need to rotate the ratchet a few times. When tight, position the ratchet handle down as in the beginning position such that the ratchet is folded.
To loosen the strap, pull on the release lever as shown in the picture below.
Then rotate the ratchet handle in the opposite direction and pull the strap out of the ratchet cylinder.