This is the 4th most frequent Russian word.
по
The Russian word "по" means "on," "along," "according to," "by," or "via," depending on context.
In this sentence, "по" is used to indicate movement along, within, or around a space, such as through or in a location.
Мы гуляли по парку.
We walked through the park.
Here, "по" is used to indicate the means or medium through which something happens, in this case, via the radio.
Он получил известность по радио.
He gained fame through the radio.
In this example, "по" is used to show a causal relationship or basis for an action, such as according to or because of something specified.