The phrase "to use the telescope" means looking through the device called a telescope to see objects that are far away in space or on Earth. Full definition
When astronomers use their telescopes to look at stars, things are different. (science.howstuffworks.com)
Each chapter includes a section on the history of observation, then the results from the space missions and methods of observation using telescopes of smaller or moderate aperture. (newscientist.com)
Most searches of objects deep in space require long time observations using telescopes. (kavlifoundation.org)