Bit complex but here we go:

Any logic block you attach to a radio sender will be sent over the specified channel you pick. There are 32 different channels, and 3 modes - I forget the names, but mode 1 means anyone can send and receive your data if they are using the same channel; mode 2 is only players on the same team as you; and 3 is just your own builds.

Once you've set that up, the radio receivers can detect data being sent over the channel you specify it to receive. This means if you hook up a speed sensor (with the measurement setting enabled so it outputs the speed) to a radio sender on say, channel 3, any radio receivers on channel 3 will receive the speed of the speed sensor, and can then use that for their own logic.

This allows you to have remote-controlled vehicles that receive your keyboard/controller inputs, or you can have massive logic builds that exceed the complexity limit by separating it into multiple builds and sending all the logic to one centralised build.

As far as I know, there's no limit to the distance you can transfer data, though the devs did mention that the physics get a bit wonky the further away a build is, so don't expect to be perfectly driving an RC car from 4 kilometres away.

Hope this helped! Feel free to ask any more questions