How does NASA communicate with spacecraft?

What is wavelength?

Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength.

The difference in wavelength is the way we tell different kinds of electromagnetic energy apart.

Figure from NASA's Jet Propulsion Laboratory's publication: Basics of Space Flight Learner's Workbook.

What are radio waves?
What is frequency?
How is data put on radio waves?
Is there energy in space?

More about radio waves and electromagnetic radiation.
How are frequency and wavelength related?
What is electromagnetic radiation?

How do you make a radio wave?
What makes EM radiation?
What other forms of energy does a spacecraft releases into space?