It means the header for the script to work, just leave it as 00 for the Unknown Header.
A script event means it gets triggered if the person steps on it.
well click on the event tap on AMap, and at the bottom it will say
Warps
signposts
Scripts
Persons
(maybe not in that order but there are 4)
and all you have to do is increase the number of the desired tiles(Warp, script, signpost, person) you want then click change events, then the tiles you added will in the very top left hand corner.
well when making a script on a green script tile, you have to put in values in those boxes or the game will freeze when you step on the tile that the screen script tile is on.
Anyways when you make a green script tile you put 0003 in the Unknown box, then put 4050 in the Var box below it, to keep it from freezing
if you want a better explanation go to thethethethe's scripting tutorial in the tuts section :D
These questions should just be asked in the simple questions thread.
Those values depend on what you're doing.
Generally, only use the first two. Just copy the values from an existing event and just paste them into yours.
Its just the same as GBA, I'm guessing the only real dif. is just its gbc. I mean, XSE is a universal script editor, not just for GBA, just look at a simple message script and it should be just about the same.