Light is collected through the telescope’s aperture and sent toward the next optical piece inside the scope. The larger the aperture, the more light is collected, which results in a greater image resolution. In a reflecting telescope, the light is then passed on to the secondary mirrors, then to the focal point. In a refracting telescope, the light goes from the main lens (aperture) directly to the eyepiece lens.
Now you might be surprised that your eye pupils have an aperture of 7mm and are doing exactly this exact job as you are reading this article. In comparison with a moderately sized telescope, say 60mm, said telescope harvest 70 times more light than your naked eye!
When you upgrade your telescope for one with a bigger aperture, you may expect the images you see through your scope to be much clearer and sharper. A greater aperture is indeed equal to a greater resolution, and thus a 10-inch telescope will theoretically separate two points in your field of view better. For example, if you are observing Jupiter, you may spot the Galileans moons more easily and see finer details.