tilebased help?

[ChaseNYC]

Alright I'm trying to make somewhat of a tilebased game... Really more so a learning experience and a way to experiment. The way I learn languages is by setting a goal and then just diving in and learning what I need as I go along and following tutorials. My acitonscript knowledge is limited and blurly, I have been messing around with actionscript for a few years but very on-and-off... I made the website www.hrprivacy.com which I'm not too proud of but has some reasonably intricate code, or at least I think so. ANYWAYS, assuming I'm not asking too much I am using tonypa's website (http://www.tonypa.pri.ee/tbw) as a tutorial and I like it very much but some of his explanations don't exactly cut it especially since there is no dialog. The following code I understand completely:

// our map is 2-dimensional array
myMap = [[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1], 
		 [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
		 [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
		 [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
		 [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
		 [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]];
// declare game object that holds info
game = {tileW:20, tileH:20};
// walkable tile
game.Tile0 = function () { };
game.Tile0.prototype.walkable = true;
game.Tile0.prototype.frame = 1;
// wall tile
game.Tile1 = function () { };
game.Tile1.prototype.walkable = false;
game.Tile1.prototype.frame = 2;

now I start to lose it in this next section:

// building the world
function buildMap(map) {

i don't understand where this term map comes in...

edit: i figured out the whole map thingy xD

	// attach empty mc to hold all the tiles and char
	_root.attachMovie("empty", "tiles", ++d);

This makes sense except the ++d, i'm guessing it has something to do with how many tiles to make?

	// declare clip in the game object
	game.clip = _root.tiles;

makes sense

	// get map dimensions
	var mapWidth = map[0].length;
	var mapHeight = map.length;

im confused about what map[0].length value would be equal to and map.length, im not sure where those come from...

the rest of the lines are the following but I guess the above is enough to try and understand for now...

	// loop to place tiles on stage
	for (var i = 0; i<mapHeight; ++i) {
		for (var j = 0; j<mapWidth; ++j) {
			// name of new tile
			var name = "t_"+i+"_"+j;
			// make new tile object in the game
			game[name] = new game["Tile"+map[i][j]]();
			// attach tile mc and place it
			game.clip.attachMovie("tile", name, i*100+j*2);
			game.clip[name]._x = (j*game.tileW);
			game.clip[name]._y = (i*game.tileH);
			// send tile mc to correct frame
			game.clip[name].gotoAndStop(game[name].frame);
		}
	}
}
// make the map
buildMap(myMap);
stop();

i hope i'm not asking too much even though this post is pretty long... I'm just trying to make sense of some of this code... thanks in advance ^^