There are two different types of telescope. The first is a tube with a lens at each end: a refracting telescope. The other one has a lens at the far end and a concave mirror at the near end: a reflecting telescope.
Here is the observatory dome. Have a look inside. This is a reflecting telescope. Here is the concave mirror. You can see it better from the top. There's another small mirror which brings the light back down here. We have a camera in here. The image is relayed to this computer here. We can see the stars on this monitor over here.
Now we will have a look at a refracting telescope. This is a small one. It has two lenses, one at each end. The large objective lens at the far end has a long focal length. The eyepiece lens has a shorter focal length. I'll show you the lenses.