In Portuguese and in many other languages, we divide actions into real and hypothetical ones. "Pode" and "podemos" indicate an action that belongs in reality, that's why they are in a verbal mood called "INDICATIVE. Ele pode te ajudar. He can help you. It is a fact. It is real. Now, if you add a "talvez" (maybe) to the sentence, you are not so sure any more. You started guessing, assuming, imagining, hoping, wishing. It is a hypothetical action, and therefore you should use another verbal mood - the SUBJUNCTIVE. Talvez ele possa te ajudar. Maybe he can help you. Another example: Podemos chegar às 6. We can arrive at 6. Espero que possamos chegar às 6. I hope we can arrive at 6. Although not very common in modern English, you can still find traces of it in your mother tongue. He is a doctor. Ele é médico. (present indicative) It is necessary that he be a doctor. É necessário que ele seja médico. (present subjunctive) Hope it helps. :)