People can choose between parties or rest, and most people choose parties, day after day, night after night. It starts forty days before Easter. It's based on the Christian calendar, but it isn't approved by the Church very well. It lasts four days and four nights. It starts on Saturday and finishes on a Thursday.
People put on their costumes and go out into the streets or to clubs.
There are also the Samba schools which make a parade showing their music, fantasies, and allegorical cars. They are followed by the people. Every year the parade tell a different story. Each city has one or more schools like this. Carnival is celebrated in the south where by Wednesday everything comes back to normal.