Look for them in the links Jura recommended, that where you can find native English language partners wanting to learn Portuguese for mutual exchange.
I would like to give you some tips to help you start learning English and improving it on the long run:
To start learning English from the scratch you might need to take some initial classes to learn the alphabet , how to pronounce ,basic vocabulary and grammar. You can do that by taking classes in a language institute or by self learning online, although some guiding from a tutor at that early stage is recommended, unless you are able to depend only on audio/video facilities.
Then you have to practice and increase your vocabulary through different means such as :
*Reading at your level of comprehension simple texts or books and looking up new words .
* Listening to English through music and possibly reading the lyrics.
* Watching movies in English with subtitles in your mother tongue..
* Chatting with natives online using voice chats or in real life .Mingling with natives is a very good way to be constantly listening to speech in English, even if you don't understand at the beginning.