Taking the bus in Belém can be a bit confusing, if you don’t know the city. The government site for the city has you covered though…for the most part. On their Public Transport page, they offer a way to track down which bus goes where and then they offer you (if you scroll down) a text version of the route or a map of the route. Either way, there are no times associated with the routes, just the street names in the text version.
The first field says “Passando em” (Passing by), the second field says “Saindo de” (Leaving from) and the third, “Chegando em” (Arriving at). From there, you enter the street you are on into one of the fields and a drop-down list will appear for you to choose the correct street. Once you’ve chosen the street, a results section will appear below where you’ll find the bus lines and an option to choose text or map.
To help you a little more in your planning, my post on the zones and bairros of Belém offers a tip on knowing which bus lines go through which neigborhoods.