Inexperto means 'inexperienced' or 'unskilled'. It's a powerful and somewhat formal word that you don't hear in every song, making it stand out.
In this song, Alejandro Fernández uses it to describe his inability to move on from a past love. The title itself, "Inexperto En Olvidarte," translates to "Inexperienced In Forgetting You," perfectly capturing the raw emotion of someone struggling to let go and highlighting the unique pain of being unskilled in the art of forgetting.
Alejandro Fernández completely drops his pride in this track, and he does not care who sees it. From the very start, he admits that moving on is impossible: "Me está costando olvidarte por completo" [It is hard for me to forget you completely]. Instead of playing it cool after a breakup, he confesses that walking away without a kiss hurts all the way down to his skeleton: "Es tu desprecio, que golpea hasta los huesos" [It is your coldness, which hits down to the bones]. He calls himself an absolute rookie at moving on with "Inexperto en olvidarte" [Inexperienced at forgetting you]. Rather than pretending he has everything under control, he admits he is ready to beg on his knees until she takes him back: "No me importaría humillarme / De rodillas suplicarte" [I would not mind humiliating myself / Begging you on my knees].
What makes this track hit so hard is how bluntly he takes the blame. In the chorus, he belts out "Hoy tú tienes la razón / Y el cabrón yo siempre fui" [Today you are right / And I was always the jerk]. Pay attention to that word cabrón. Depending on where you are in the Spanish-speaking world, it can mean anything from a tough guy to an outright insult, but here in Mexico, he is flat-out calling himself the selfish jerk who ruined the relationship. There is no sugarcoating or making excuses. He puts his hands up, names himself the loser ("me declaro perdedor" [I declare myself the loser]), and admits that any tough front he puts on is total nonsense.