Traveling by bus will be a huge experience for  new missionary.  I have compared the Brazilian bus station to the United States' international airports.  At the bus station busses leave every fifteen minutes with destinations to all parts of Brazil an near countries.  There are 2 kinds of busses in Brazil, urban busses and travel busses.  The next picture is a picture of an urban bus.

This is the bus I took to go to the airport.  It is comfortable. (executive bus) 

There are 3 kinds of urban busses.

1. Commercial
2. Executive
3. Leito (bed)

Commercial should be called common.  It is not fancy, generaly does no have a facility and stops a lot along the way.  Executive has a fancy, but is very similar to commerical except it has a few extras.  Air conditioning, water, facility, more comfortable seats.  Now for leito or bed.  There are 3 seat across rather than  4, they go way back, and seat half as many as the other busses, hense the price is 2x.  Now I nver used one of these on the mission, but I have taken advantage of one after the mission.  Since the executive bus is only 2-3 dollars more, I would suggest taking that, but don't get a seat un the middle, that is right under the A/C and  you may freeze oh and sometimes condensation drips down.  

This is right inside of the Bus Station, to the right is the enterance, to left is the waiting area.

This is the waiting area.  10 minutes before departure the busses arrive and you decend the staires to under the waiting area (this picture was taken from a stairway).

This is an arial vies of the Belo Horizonte bus station.