Some very basic Soccer concepts and rules.
1. Not using hands (except the Goalie) and not tripping, holding, pushing or hitting other players (it is good to "fight" for the ball, but not to use hands to hit or push).
2. The concept of a "field" that has lines that you and the ball should stay inside.
3. The concept of "our goal" (the one our Goalie is in) and "their goal" (the one the other team's Goalie is in) and that when we have the ball we should go toward "their goal" (to "attack" it) and when the other team has the ball we should "defend" our goal by kicking the ball away from it. Demonstrate what this means in a slow and patient way and repeat it in several practices.
4. The concepts of "attacking" and "defending" and how we try to kick the ball into the other team's goal and how we try to kick it away from our goal.
5. The very basic idea of "positions" and that some players play in different areas of the field and don't just run all over the field (e.g., that there is a "Goalie", "Defenders" and "Scorers").