im planning go on a trip to USA from Brazil in june, i have the intention to buy eletronics while there to bring back to Brazil, a videocard, motherboard and such, what i must do? there is a fee of some kind?
They are called "import duties" in English, and every country sets its own rates. The Portuguese term appears to be "Imposto sobre a Importação"; perhaps you can find an official Brazilian government website.
There is usually a "duty free allowance". If the value of your purchases is more than this amount, then you will need to declare your purchases at customs when you enter Brazil. If it's like most other countries, the customs officials will determine the value of the goods (it will help if you can show the purchase receipt) and tell you how much you owe. You should be prepared to pay on the spot, or else the goods may be held at the airport until you come back and pay later.