Hello Lavatan,
In picture ...13, the square shaft on the top is a clutch for the recoil starter. Give it a spin by hand and it should turn freely in one directon and catch the crankshaft and turn the engine
in the other direction. The bottom have of this starter clutch screws onto the crankshaft. Remove the 4 small screws on the bottom half and the top half will pull off revealing 5 loose balls.
remove the balls. Then take a medium to large flathead screwdriver and put the end on the screwdriver against on of the tit's on the edge of the bottom half of the clutch and hit it with a
hammer to loosen it (counter-wise). After breaking it loose unscrew and remove the bottom half. The end of the crankshaft is tapered and there is a woodruff(half-moon) key that the flywheel
fits down on. Using 2 large screwdrivers or small pry bars pry up on the bottom of the flywheel and it will come off the crankshaft. Be careful about where these prybars touch the flywheel and
engine block because it is easy to damage either of them. It is also possible to do damage to the bottom of the starter clutch when using the hammer/screwdriver so be careful there as well.
Once you do this you will know the "trick" and it will be simple from then on. This assemble is common to most briggs and many other brands of small engines with recoil starters. Your particular
engine could also be equipped with an electrical starter motor. That starter clutch tool from Amazon looks very useful as well but I've never owned one. It's actually quicker to do than to read
all this.