Hi Pedro, "Tune in" means "start to watch (or listen to)". "He tuned in to the sports channel / BBC radio" = He started watching/listening to the sports channel/ BBC radio.

Tune in is only used for broadcasts like television. It refers to setting the channel on an old analog television. It’s slang and a bit outdated. You wouldn’t really use this unless you were doing a commercial. I hope that helps, Bob

Seria a diferença entre assistir algo (watch) e "colocar no canal" (tune in), sintonizar no canal.

No

I don't know very well but I think You can tune the frequency for examples in your tv it is soemfing like setting you channels in tv and you can watch tv and it is mean just watching tv.