This is an optional video, it shows a new sword technique and some kinstones fusions. I recommend 'hunting' for some kinstones on South Hyrule Field, and when you get some of them, you can try to fuse kintones on Hyrule Town.
Try to fuse kinstones with the max number of persons, but you don't really need to, since you will be able to do it later on the game.