You stand facing each other, with your legs slightly wider apart than shoulder width.

Then you grip each other's right hands firmly. This is done almost as you would to shake hands, but the assisting partner holds the weight-bearing hand palm-up. (If it were palm down, you would just slip right out and crash to the floor.)

Trusting them to hold you, you lean over your own arm. If your right hand is being held, you extend your left hand over the top of the fulcrum of your (and your partner's) arms.

You leap over (while your friend takes your weight for an instant) and you breakfall on your side.

The your left arm (or whichever one is not being held) slaps the mat as you land.

Occasionally, during your training sessions, someone's grip will slip, and they're going to drop you in the middle of a Kotegaeshi breakfall. You need to develop your skill to cope with this, too.