What does “je n’arrive pas à” mean in French?

Arriver à plus an infinitive has nothing to do with arriving: it means managing or succeeding. So je n’arrive pas à is the everyday way to say that something is defeating you right now — je n’arrive pas à compter sans mes doigts, je n’arrive pas à dormir, je n’arrive pas à ouvrir ce bocal. It reports effort and difficulty, not permission or lifelong ability.

Compare je ne peux pas (“I can’t / I’m not allowed”) and je ne sais pas nager (“I never learned to swim”): je n’arrive pas à nager means you are in the water and failing. The positive side is just as useful — j’y arrive ! (“I’m getting there!”), tu vas y arriver (“you’ll manage it”), where y stands in for the task.