It's common to hear from Brazilians that the new year only starts after carnival, this is partially true.
Since Christmas holidays coincide with Summer vacations, schools are closed from middle of December and during the whole month in January. If Carnival season happens to be in the beginning or in the middle of February, then expect people to be on vacation for most of that time.
December is a very special month for Brazilians because people get excited about the commercial celebrations around Christmas, like the exchange of gifts, parties, decorations, and all the things related to that, such as buying new clothes or even new furniture.
The thirteenth salary boosts the economy. Summer season officialy starts on December 21st in the Southern Hemisphere and Brazil is bursting with tourists. The excitement about the réveillon (new year's eve) grows each day, that's like an anticipation for the Carnival season in February.
A very popular way to exchange gifts is the amigo secreto (secret friend) game. About one month before Christmas, people write their names on tiny pieces of paper and make a drawing among themselves, the name you draw is the person you have to buy a gift for.
It's very important to keep it in secrecy!
On the day of the party, the people gather in a circle to give the gift to their secret friends. Usually they play a guessing game, by stating "my secret friend loves chocolate and comics, he's also very talkative, etc." so everybody guesses together. It's a lot of fun!
The response to that is the amigo da onça (jaguar's friend). Amigo da onça is exactly the same game, only that you get mock gifts, which is always hilarious.
Amigo da onça is meant only to be played amongst real friends, who really know each other and truly like each other, this should be by no means used in a way to indirectly hurt somebody.
For the réveillon people flock into the beaches. The weather is just perfectly warm and the sky is clear for the spectacle of fireworks. It's not uncommon to have a huge stage on the beach where bands perform all night long to celebrate the new year. The color of choice to wear on that day is white, which symbolizes peace.
The most important message for the new year in Brazil is that one, peace in the world. There are all kinds of supersticious rituals like wearing red underwear if you wanna find the love of your life, yellow underwear if you wanna earn much money, green underwear for good luck... Some also skip 7 little waves on the beach for good luck. They drink sparkling wine and cider and celebrate all night long.