It means your reading material should be about 1.33 meters away from your eyes. With this kind of Reading glasses on you will feel comfortable to focus on your reading material and the letters will look as large as they always do when they are 1.33 meters away from your eyes.
The number 0.75 indicates how serious your presbyopia is, it is the same as myopia. Different people have different degree of presbyopia and they need reading glasses in different power. If you have slight presbyopia, then 0.75 reading glasses may be good for you.