Radio telescopes are large dish antennas designed to collect long, lazy radio waves. Radio waves also shine right through Earth's atmosphere, so putting these telescopes on the ground works fine.
Although radio waves are long, they still move fast, at the same speed as light. Radio waves can be used for lots of different things. Our TV, radio, and cell phone signals are carried by radio waves of specially selected wavelengths. Other wavelengths can be used to look out at our Universe to learn about planets or galaxies. Yet others are used by NASA's Deep Space Network of antennas to detect the faint radio signals from spacecraft traveling to faraway destinations, like Mars. We use these radio waves to send messages to our spacecraft and receive information from their special instruments.