Remember that the language of Brazil is Portuguese and, in spite of what some people think, Portuguese is not a dialect of Spanish or of any other language. Portuguese is a separate and distinct language. If you know some Spanish, you can certainly try to make your wants or needs known using Spanish. While Portuguese and Spanish are linguistic cousins and some Brazilians may understand what you say in Spanish, they probably will not answer you in Spanish.
Even if you are a Portuguese "beginner," learning and using simple Portuguese phrases with confidence can go a long way in demonstrating respect for Brazilian people and culture. Phrases like thank you (obrigado for men, obrigada for women), no thank you (não obrigado for men, não obrigada for women), por favor (please), com licença (excuse me), prazer (pleased to meet you), desculpe (sorry), bom dia (good morning), boa tarde (good afternoon), boa noite (good evening/good night), adeus (goodbye as in forever) or the even more commonly used tchau [pronounced like the Italian ciao] (goodbye) as well as other simple courtesies will be very much appreciated by most Brazilians.
Brazilians readily adopt words from many different languages including English. Words and phrases such as shopping (shopping center/mall; plural = shoppings), moto boy (motorcycle delivery driver), lite or light (light or lite foods or drinks), mouse (computer), sexy, happy hour, and many others have found their way into the Brazilian vernacular. They are regularly used and understood by Brazilians, although the pronunciation is most often very different. In addition, the spelling of many Brazilian Portuguese words are somewhat similar to their English counterparts so it is possible to 'wing it' and get by using English and a few Portuguese phrases (up to a point).
When speaking English to almost any Brazilian who says they know the language, it is best to speak clearly, slowly, and use simple words. Avoid using slang and colloquial expressions and, by all means do not assume that they really understand what you are saying in English. Brazilians are generally very polite and want to please you by showing that they understand you...even if they really don't. If you see a glassy-eyed expression accompanied by a smile when speaking English with a Brazilian, you may want to rephrase your statement or question.