The first telescope to be invented was a refracting telescope. A refracting telescope works by using converging lens to collect light. A refracting telescope has a convex lens that bends the parallel light that is coming into it to a focal point. That focal point is where an image is formed of what is being observed. At that point is the eyepiece that you look through to see the focused image. This diagram shows the inside of a refracting telescope.
A reflecting telescope was invented after that refracting telescope by Isaac Newton. A reflecting telescope works by collecting light and reflecting it off of a concave mirror. The light that is reflected comes to a focus point where a flat angled mirror reflects that light up toward an eyepiece where the viewer sees the image. This diagram shows the inside a reflecting telescope.