You can view in-game scripts by downloading XSE v1.1.1 (Make sure it isn't v1.0!), opening it through A-Map by selecting 'Settings > Choose script editor' and then navigating to wherever you saved XSE on your computer. Now when you double click on a sprite in A-Map, it will open that character's script in XSE. This is the best way to view scripts in-game, but if you want to make any additions like inserting more text, or adding a completely new character from scratch, you should learn how to compose a script. You should only edit already inserted scripts if you
know that you're going to take up the same amount of space or less, which can be hard to judge if you're just starting out.
Scripting is basically just a series of relatively simple commands that are read by the game and then executed sequentially. This means that a lot of tutorials just focus on explaining the commands and giving some examples of how/ when they're used.
diegoisawesome's tutorial is pretty much the standard if you want to learn how to script as it has pretty good explanations for most of the commands and uses plenty of examples.
Avara also has really good tutorial, though it isn't as long as diegoisawesome's.
Spherical Ice's repost of DavidJCobb's scripting commands is also good for explaining the technicalities of some of the more obscure commands. If you're more of an audio learner/ want to see scripting in real time,
Anthroyd has a series of videos about how to hack, some of which specifically focus on scripting.
My most important piece of advice when learning how to script is to just play around with it for a while until you get the hang of it. Don't immediately try to make a hack while getting the fundamentals down as you'll just be compounding any frustration you experience. Just use a blank ROM and make a couple of basic things like a signpost/ trainer/ tile script that do different things. Do this for a couple of hours and when everything seems to be going smoothly, you can go back to trying to make your own hack. Good luck!
