The only official language in Brazil is Portuguese. However, it differs slightly from Portuguese spoken in Portugal. So if you intend coming to Brazil and staying for a longer period, you should pay attention to learning the “right” Portuguese beforehand.
Portuguese is spoken by almost the entire Brazilian population which means that there are around 190 Mio. speakers in Brazil alone. In addition it is the official or co-official language of 9 further countries and the number of speakers worldwide is over 240 Mio.
Besides Poruguese, there is also a high presence of Indian languages in Brazil, mainly in the northern regions of the country. Yet except for a few isolated indian tribes, Portuguese is the main and only language of communication. Some immigrant communities, mostly Italian and German, established in Brazil at the end of the 19th century, still preserve their language to a certain degree. So if you are in the south of Brazil, where these communities are located, you could be addressed in your own language.
Due to Brazil's rising importance in the global market, the importance of Portugues as a world language will rise. If you are going to Brazil only for a short period and thus think that learning Portuguese is not worth the effort, you might miss a chance of gaining valuable qualification which might help advance your future career.
Do not think that you can get away with speaking English in Brazil. The number of Brazilians speaking English is very low. If you speak Spanish you will be able to understand and to communicate with the locals on a certain level but some Brazilians might get offended when being spoken to in Spanish.
On the other hand Brazilians will highly appreciate if you try to learn and speak Portuguese, even if it is on a basic level. As they are very friendly and communicative speaking their language will help you make many friends and establish important business contacts if you put some effort into learning Portuguese.
When the Portuguese arrived in the area of South America in the 16th century, which is now Brazil, their language met the main local linguistic family, Tupi-Guaraní, in particular the Tupinambá dialect. Over the ceturies the different dialects intermingled with Portuguese. Further enrichment to the language were brought by the various dialects of African slaves.
This led to the differences between Brazilian Portuguese and that spoken in Portugal. It is mainly based on pronunciation differences. Whereas the European Portuguese sounds quite rough, Brazilian Portuguese is very nasal and thus appears softer. Other differences appear in the lexical. There are different words for the same item in European and Brasilian Portuguese. The same word can refer to two different items. Other significant differences can be found in the orthography. Words which in European Portuguese contain a cc, cç or ct but also a pc, pç or pt are reduced in Brazilian Portuguese to the last letter only.