Ok, lets start simply. void creates a new function.
Anything in OnStart is a function that will either need to be detailed in its own void, or finalized right there in OnStart.
OnEnter are things that happen every time you enter an area.
OnLeave is every time you leave.
http://wiki.frictionalgames.com/hpl2/amn..._functions
Should help a bit, but you just need to think of XML as being a ladder. You place the top of the ladder, then you need to fill in the missing rungs right down to the bottom. This can be hard to learn, but its easy once you know how its done.
Also, the community will assist you if you need a particular script written, as long as it isnt too complicated.
Also, the actual games scripts can make an excellent point of reference
Best of luck