Pile in happens any time at the end of a combat being resolved where neither side of the combat has fled due to failed morale check, and neither side has been entirely wiped out.
any models that aren't in base contact with atleast 1 opposing model moves up to 6" to become in base contact. (both players take turns in doing this)
It's really quite simple and the rulebook is very clear, I don't think you will get much help in explaining it short of maybe getting lucky and having someone explain it in dutch
Mattlov wrote:You pile in AFTER the first round of combat
untrue, you pile in in any round of combat which satisfies the conditions for a pile in.