It takes two men to operate each bus in Goa. There is the driver who's responsibility is to drive recklessly fast and honk at all the cars, scooters, and cows in the road. And there is the fare taker.
The fare taker walks through the bus collecting fares once the bus gets moving. He also calls out the destination of the bus repeatedly at the depot to collect more riders. Along the route he will open the door for people standing on the side of the road calling out the destination again.
The bus will let people off pretty much anywhere, but there are designated bus stops to pick up more people. Hopefully, you can jump on before the bus starts up again.
Bus depot in Mapsa, Goa