Your Spanish already covers a lot of Brazilian Portuguese. Here is what carries over, what only looks the same, and which sounds to learn from scratch.
A head start, with a few traps
Regular spelling changes turn many Spanish words into their Portuguese form. They are tendencies rather than rules, but they hold often enough to make a good guess.
These words look like Spanish but mean something else. Falando points them out in practice when an answer uses the Spanish meaning.
Most nouns keep their Spanish gender. These common ones switch, and the article and adjectives switch with them: o nariz grande, a ponte nova.
One rule covers many of them: nouns ending in -agem are almost always feminine.
Spelling is where Spanish helps most and pronunciation is where it helps least. The approximations use Spanish spelling and follow the accent of most of Brazil.
Falando can mark the words that look and mean the same in Spanish as already known, so your reviews go to false friends and new vocabulary. You can turn this on or undo it any time in Settings → Learning → Manage progress.