Wow that's a mouthful.
Scroll up a few lines and look at the header (reprinted here for convenience)
Code:
// ----------------------------------------------------------------------------------
// Syntax :
// [Frqequency] [ItemGroup1] [ItemGroup2] [ItemGroup3] ...
//
// Itemgroup = [Item(hex)] [ZLevel(dec)] [Color(hex)] [Xmovement(dec)] [Ymovement(dec)]
// ----------------------------------------------------------------------------------
//Probably some babble by me.
//Probably some babble by Ry.
// Peach Tree with green leaves
0001 0d9c 0000 0000 0000 0000 0d9d 0000 0000 0000 0000
The first number is the "weight" it is not exactly a percentage. Only Darus knows exactly (maybe Syd if he has the source). It is more akin to a piece of paper thrown in a hat for each number. So the percentage depends on the numbers of all the weights added up.
Then as you noticed you have the item id, then (see header above) the Z offset. This is how far or below the terrain. Then the color if not default (I'm not sure if it works or not) then the X and Y offsets. So for example:
Code:
//Cedar tree small group
0003 0cd6 0000 0000 0000 0000 0cd7 0000 0000 0000 0000 0cd8 0000 0000 0002 0000 0cd9 0000 0000 0002 0000 0cd6 0000 0000 0001 0002 0cd7 0000 0000 0001 0002 0cd8 0000 0000 0000 0002 0cd9 0000 0000 0000 0002 0cd6 0000 0000 0001 0003 0cd7 0000 0000 0001 0003 0cd8 0000 0000 0003 0003 0cd9 0000 0000 0003 0003
That makes a small group of cedar trees around the spot that is picked (that one is courtesy Ry I think).
If you don't want something you can remove it altogether or comment it out with "//". I'm not sure about giving a weight of 0000; try it and let us know. At any rate it is better to comment it out, one less line to parse.
Thou can addeth and thou can taketh away from the scripts to your heart's delight. You can make new scripts and call them whatever you like.
Items.txt is where you get Dragon to place them. Which leads to your second topic. Again read the header and all will become clear. I am not going to say anymore because if you do a search I think you'll find a post I made about items.txt that Ry saw fit to tutorialize.
The files that get created you run through DragonSP, the second half of Dragon. Doing multiple compiles and keeping parts of different ones is an advanced topic, also been discussed at length here; do a search.