Toca fita literally translates to "plays tape" but refers to a cassette player. It's an interesting and somewhat nostalgic term that evokes a specific era of music consumption.
In the song, it sets a scene of intimacy and shared memories, as the couple listens to their favorite song on an old-school cassette player in the car. This detail adds a unique charm and a touch of vintage romance to the lyrics.
Bryan Behr sets this one in a car, at night, somewhere between two people who are about to say goodbye. He opens with 'As estrelas mais antigas / Brilham muito mais bonito ao lado teu' [The oldest stars shine so much more beautiful beside you] and immediately narrows the whole world down to a tape deck and a chosen song: 'No teu carro o toca fita / Toca a mesma faixa que você escolheu' [In your car the tape player plays the same track you picked]. That is the whole scene: driving nowhere in particular, lying on the ground to look at the sky, learning someone by the music they chose for you.
Then the chorus turns the song itself into the trigger. 'O rádio quando toca / Aquela canção bonita / Faz molhar os olhos e adiar as despedidas' [When the radio plays that pretty song, it makes your eyes water and puts off the goodbyes] - the favorite song does not just remind him of her, it physically stalls the moment he has to leave. By the time he is just repeating 'Faz chorar' [It makes me cry] over and over, there is nothing left to explain. Some songs do that: not sad exactly, just heavy enough that you would rather stay in the car a little longer.