In English we use a He is/ We are/ You are/ They are/ I am. In Hindi these mostly match up with what we use in English वह है/ हम हैं/ आप हैं/ वे हैं/ मैं हुँ. है=is हैं=are हुँ=am. तुम is an exception because it matches up with हो which means “are” in this case.
Yes you are correct. Lately तू and तुम are very much interchangeable and mean almost the same. In formal settings it must be आप just like vous in French or Usted in Spanish. In other words, one must use आप with strangers, older people, parents and teachers etc.