[Luigi203]

tiles[x,y] just gives you the tile index at x and y. Tilesets are broken up into 16 x 16 pixel 'tiles', and each tile has a unique index. This is just used to read and write these indecies. Experiment with it,

function OnMouseDown() {
player.chat = tiles[mousex,mousey];
}

to check tile indecies, and you can write them like so

function onMouseDown() {
tiles[mousex,mousey] = #;
}

Hope this helps..