layer's width and height. You use BGPUT layer_number, x, y, tile_id to put the tile tile_id at position x, and y on the layer. Note this is in tile coordinates not pixels by default. You can use BGGET layer_number, x, y, tile_val to read the tile at x, y on layer tile_layer and save it to the variable tile_val. You move layers around with BGOFS layer_number, x, y to move a layer around so x, y