Ramon, like in all countries, the choice of terms to address people is not always a clearcut thing. We use "o senhor" or "a senhora" very frequently in Brazil. At home, for instance, there are people who address their parents in these terms. I don't, but I used to call my grandmother that. It depends a lot on the internal culture of the family. In non-domestic contexts, like at work, you assume it is appropriate to address those above you at the corporate ladder with "o senhor" or "a senhora", unless they tell you not to. There may be tricky situations, like when the boss is much younger than the enployee, and often the boss tells the emplyee not to bother. On the street, you address an elderly person, for example, normally with "o senhor" or "a senhora". Very often they tell you not to bother, so then you may drop it. This is my rule of thumb: if in doubt, use it. If your interlocutor does not care about it, they will normally tell you not to bother. Hope to have helped you and wish you all the best with your studies of Portuguese.