Descifrar means "to decipher" or "to unravel". It's a less common verb that suggests a deeper level of understanding or solving a mystery, rather than just simply understanding.
In the context of the song, Ana Torroja sings, "No es fácil descifrar una intención" (It's not easy to decipher an intention). This highlights the difficulty in understanding someone's true feelings or motives, adding a layer of intrigue and complexity to the relationship she's singing about.
"Antes" is about the moment just before a difficult conversation, and the wish to stay in it a little longer.
The singer asks for something small and hard: look at me for a second before we start talking. She wants what is between them to be real, and she wants the doubt that keeps circling to go away. So she tunes out everything around her and tries to feel a warmth she says nobody has any more.
The middle of the song is honest about how little she can read. It is not easy to work out what someone means when you are both lost in confusion, close and distant at the same time. She waits on her side of a wall they built together, wanting to see what is behind it, hoping it can still work.
By the end she has her answer, and it comes from silence rather than words. Time stops in his eyes, she listens to the quiet, and she says she understands. The song closes on the same request it opened with, which now reads less like hope and more like goodbye: let's look at each other for a moment, before we start talking.