Mañas refers to tricks, cunning habits, or street smarts. While it can literally mean "skills" or "bad habits" depending on the context, here it represents the unspoken rules of the hustle.
In this rags-to-riches song, the singer warns, "En el juego muchas mañas, uno tiene que estudiarle" (In the game there are many tricks, one has to study them). It is a fantastic vocabulary word that perfectly captures the gritty theme of needing sharp street smarts to survive and earn a "billete grande" (big bill).
This song is a classic corrido story about coming up from nothing. The singer starts by telling us just how rough things were: he was so poor he walked barefoot until his feet burned, caminando por la calle descalzo, los pies me arden (walking barefoot in the street, my feet burn), and prayed to saints while he was starving. He knew he had to be the one to change his family's situation because he had big dreams and wanted billete grande (big bills).
Now, things are totally different. The phone is ringing off the hook with business, and he says Ahora va la mía, ya no doy vuelta pa' 'tras (Now it's my turn, I'm not turning back). But this success came at a cost. He talks about the dark side of the business, how friends won't teach you the secrets and want to see you fail. He also mentions a deep personal loss, a traumatic night when his brother was killed. The song ends with a shout-out to the Guzmán Salazar family, a direct reference to El Chapo's family, making it clear what kind of world he's moving in.