A radio telescope is like a huge satellite dish. An ordinary telescope allows people to see light from distant objects. Stars shine and the light can be seen with a telescope, but they also give off radio waves. Scientists with radio telescopes receive these radio waves and use computers to learn about the stars. Other things like black holes also give off radio waves and radio telescopes are useful for learning about them too.
The dish is sometimes constructed of a conductive wire mesh whose openings are smaller than a wavelength. The information received by several radio telescopes in different places can be combined. This gives similar results to having a single dish as big as the distance between the telescopes, so even very faint signals can be received. Scientists are also trying to do this with ordinary telescopes.