When people think of telescopes, the type that they are probably referring to is a refracting telescope. The first ‘telescope’ ever used was created by Hans Lippershey, a 17th century spectacle maker. There are many stories going around how he discovered the refracting process but whether it was an accident or intentional is unknown. He figured out that things look closer when looking through two lenses so he invented the Dutch perspective glass, later called a telescope.
The Dutch-style refractors consisted of a convex and concave lens placed in a tube between the viewing port and the end of the telescope; therefore, the scopes did not invert the image making everything appear upside-down. The original design was only able to see 3x magnification but the Dutch were able to make considerable number of these and eventually they were all over Europe.
Galileo Galilei improved upon Lippershey’s invention by creating a telescope with a convex lens at one end of a leaden tube and a concave lens at the other. He was able to increase magnification from 3x all the way to 33x; the latter incarnation allowing him to view Jupiter and the four Galilean moons. For the first time ever, man could see into space with more clarity and detail. The rest, as they say, is history.
Early refractors were limited by chromatic aberration created by imperfections in the lenses used. This effect was minimized by making the tubes longer and longer but eventually, impracticality made it difficult and expensive as some of the tubes were reaching lengths of 150 feet.
Even though you can still get a refracting telescope, reflecting telescopes have all but replaced refractors for astronomical research.