In this game mode your objective is to get the highest possible score. This is done by packing the rectangles in the left strip.
To get a good score you need to achieve the minimal possible height. Your are competing against an algorithm. It has the same objective as you.
In the middle of the screen you see your inventory. This is all the rectangles that you have yet to pack. To pack one of these simply drag it to your strip.
In the right hand side of the screen you can see another strip. This is the strip where the algorithm packs its rectangles. The algorithm has the same inventory as you do.
After you have placed a rectangle the algorithm will do the same. The numbers that appear in the inventory is the order of which the algorithm has selected the rectangles.
You can always open this again by clickingin the top right corner