To visit Brazil you must have a valid passport within six months of your travel dates.

If you are a U.S. citizen, you must have a visa to enter Brazil. To obtain a visa contact the Federal Republic of Brazil Consulate at one of the locations listed here.

Generally this takes a couple of days - as little as one day if you pick your visa up in person. Make sure you call the consulate and ask what you need to bring before you show up in person.