Hello fellow Space Traveller,
There is this wonderful thing called the electromagnetic spectrum which describes all possible frequencies of electromagnetic radiation in our universe.
On one end of this range we find the short wave length gamma radiation, and on the other end we find the long wave length radio waves. We tend to use the radio wave length to communicate with astronauts since its too far to shout (I think the late Neil Armstrong tried it, but as far as I know we never heard it).
Somewhere in the middle of this spectrum we find the visible part of the radiation that allows you to read this post. If anything is unclear, just shout.