How to limit

#1 Just set up the MissionArea object in you level with the editor. According to the docs, when the player enters/exits the mission area, two callbacks, namely onEnterMissionArea and onLeaveMissionArea, are triggered.

#2 Can i just do that with only an object or do i need to put programming into it. In other words is the onEnterMissonArea and onLeaveMissonArea already in the code or should i program it?

#3 You need to provide (script) funktions called onEnterMissonArea, onLeaveMissonArea that handles what you want shoudl happen when the player either leaves or enters the mission area.

In Battlefield (my favorit game) the user is shown a warning that they are deserting
and take penelty if they remain out side the mission area to the point when they die.

This is a nice way to restrict players inside the mission area because it doesn't
provide an "invisible wall" that the user cant get passed (which would be another
way to do it).
Invisible walls destroy the game illusion imho :-)

#4 If it is an outside aria but fences or mountains to keep players in.