You need to visit the TV Tower to see all the Brasilia city.
Maybe you should go to the JK Memorial to learn about the president JK, it’s near the TV Tower.
Don’t forget to go to the Cathedral to see the architecture. It's a very nice place.
After, you could visit the other places in the Esplanada dos Ministérios (Palácio do Planalto, Palácio Itamaraty, Palácio da Justiça, Congresso Nacional, Panteão da Pátria, etc). In that place have many options to visit.
Don’t forget to take a camera.