Kaeshi Kumite is pre determent exercise in fighting - attacking and defending. Other example of this type of training are Kihon Ippon Kumite and Juu Ipon Kumite. But Keshi Kumite is the only fighting exercise, where the attacker wins.
For Kaeshi Kumite, the attacker and defender both start in free stance. The attacker is allowed to start with left or right site, making this harder on the defender.
The first combination in Kaeshi Kumite is called Jodan. It origin is in the Japanese name oi-zuki jodan, the first move of the combination.
The combination starts, as mentioned, with both people in free stance.
The attacker is going to be the one that starts, and the defender will be the other person.
The attacker declared the attack ("Jodan"), and then attacked, by stepping forward and punching with the oi-zuki jodan with the same arm.
The defender steps back with the opposite leg, than the opponent stepped forward. If he stepped and punched with right hand and leg, the defender steps back with left leg. With the opposite side, that the one stepping back, he blocks with age-uke. The right hand to the stepping back left leg and vice-versa.
The defender then steps with the back leg forward, attacking oi-zuki with the arm on the same side.
The attacker moved to the side (45° to the previous position), so he is on the inner side of the opponent. In practice, that means, that if he attacked with left hand, the attacker moves back with the forward leg. He blocked, or just guide the arm so it doesn't hit him with tate-shuto. He counterattacked with jako-zuki.
Both the attacker and the defender move to the free stance.
So the combination in short: Attacker: oi-zuki jodan forward Defender: age-uke back, oi-zuki forward Attacker: tate-shuto 45°, jako-zuki
So now you can try it as well, just make sure to not injure anybody.