The complete tutorial with text and screenshots can be found here: https://www.codeandweb.com/texturepacker/tutorials/getting-started-with-starling-a-flash-game ...

GIMP plug-in to create a spriteatlas (aka spritetexture or spritesheet). Takes all layers as images and compiles them into one sprite atlas texture, using a 2D packing algorithm so that the final ...