Hey, welcome to the forum :)
Figuring that terrain generation would be the hardest thing to achieve for me at first, I went ahead and got started.
If you're not familiar with how events work, procedural generation is kind of jumping in to the deep end. I think it's best to start with simple projects and build your way up from there, otherwise you will quickly get stuck!
o here's question #1 (of many, many to come): how on Earth do I fill an array with variables?
It all comes down to setting up some events that call the 'Set at XY' action (for a 2D grid, anyway).
oes it start filled with 0?
Yep.
nd how do I key each number to be relative to a sprite?
Do you mean actually creating the sprites from the data in the array? A 'For Each Element' (on XY axes) event should do that. Each iteration compare the current number in the array, and create a sprite based on that number. Subevents are good there.
I was going to explain this, but I just added it in to your capx. Try this: http://dl.dropbox.com/u/15217362/tileengine.capx
You should be careful about creating lots of sprites, though. Having too many sprites can slow down the game a lot. I'd recommend waiting until the next release or two when we add 'snap to grid', then maybe put it together in the layout editor, using tiled backgrounds wherever possible for large areas of sprites. Otherwise, the sheer sprite count could slow down performance.