You make your square with the rectangle function by its center, this will automatically draw you the two hypotenuses that connect the corners .
You can choose from one side of the square or the hypotenuse depending on the exo you are asked to do.
You select your two hypotenuses and you put an equality constraint on them (so you are sure with a single odds to have a perfect square. Better because in your case you have the two short interrupted strokes at right angles , if you put an equality constraint between them, you will also have a perfect square without the need to side the second side.
You make a sketch leave in the four corners but you take care to uncheck the function on the side of all the rays. You will then have a single rib for the spokes. Depending on what you are asked to do, you can complete the dimension with the mention "four equal rays", generally R5 x 4.
It's not because only 2 appear on the plan that we are forced to use only 2 to design (even if personally, I tend to favor relationships more than dimensions)