Prepare the trailer hitch and coupler

Raise the coupler so that its bottom is above the hitch ball. It is best to use the trailer tongue jack if you have one.

Lightly lubricate the hitch ball and inside of the coupler with automotive bearing grease.

Make sure the coupler is still above the hitch ball so that the ball can slide under the coupler

Open the coupler lock. Ball couplers have a locking mechanism with an internal moving clamp like piece, and an outside wheel, handle, or latch.

In the open position, the clamp underneath the coupler opens, allowing the coupler to drop fully onto the hitch ball.