Dumb question about running at a track

[GeeReg]

I've never raced before or even driven on a track, and I had a question about radios. How do people manage not to interfere with each other on the same channel? I know/think there is a board with tags for each channel, and if a certain channel is missing, it's in use, but how do you test/work on things in the pits if you can't even turn your radio on? I just don't see how this works.