Cuéntale literally translates to "tell her" or "tell him." It's the imperative form of the verb contar (to tell).
In the context of this song, the artist is repeatedly urging someone to "tell her" about their past intimate relationship, specifically about being her "first time" and the one who "made her a woman." This repeated command makes the word central to the song's narrative and gives it a provocative and memorable quality.
Blessed's "Cuéntale" is a super direct and confident reggaeton track where the singer is basically telling a woman to go tell everyone about their passionate connection. He's especially focused on her telling people he was her "primera vez el hombre que te hizo mujer" [first time, the man who made you a woman]. It's all about this intense, physical relationship they share, and he's not shy about wanting her to return to his room.
The song is full of playful, almost demanding lines like "ponte en posición no es que yo te quito el pantalón y tranquila suéltame" [get in position, it's not that I'm taking off your pants, just relax and let go]. He's really into the idea of them being together, just the two of them, enjoying each other's company, and he's pretty possessive, saying things like "no se aguanta que te toquen que te abra sin que te miren me sofoca" [I can't stand them touching you, hugging you, looking at you, it suffocates me]. It's a bold and energetic song about a strong, undeniable attraction.