Drokar, start with one thing, when you are stuck at a point after trying, post it here and we will help. That way you will be able to learn faster, and we can help you with what "you" are doing wrong.

A text rpg isn't exactly the easiest first project, but it is not that hard either, unless you over-complicate things for yourself. Don't bother with a save/load system yet, you can easily include it near the end, but if you really want to know, then simply search in google for a SharedObject tutorial. This would be a good read

As for writing variables, I would really advice staying off the timeline, but XML is not where you declare variables.....XML is a fancy way to declare an nested array, which is mostly used to define your game/level structure. like
Code:
<game>
   <level requiredExp="0">
       <monster count="10" maxHealth="200">
       <treasureChest count="5" maxValue="50">
   </level>
</game>
You can then read in this data to generate your game levels. w3schools has excellent info on XML, and kirupa.com has nice tutorials on dealing with XML for flash. But before this, the first thing you need to do, is perfectly plan out your game. Like how many screens there will be?(story,dungeon,fight,shop,...e.t.c), and what each screen's looks and purposes are? Then plan out the gameplay in your head, and see where, if at all, you need XML. Then its time to write the various as3 classes for your game elements, and you will declare your variables within these classes.