Stand at a comfortable distance between you and start to hit each other once each. The partner has to stop the hit with a strike of his own that effects the body but does not affect the arms. After a while do the same for the legs alone and after that combine the two and add body hits. all parts of the body are open to hit with and to but remember to end the fight is the goal and not to win it.  Keep clear of the line approach that you can only come at someone from the front ot from this angle or another. There is no needed expalantion for this.