Use ser de plus the place: sou de Lisboa. With a country the article usually stays and fuses with de - do Brasil, da França - though a few countries take none, like Portugal. Nationality words agree like adjectives and are lower case.
Examples
- Sou de Portugal, do Porto.
- I'm from Portugal, from Porto.
- Ela é brasileira e eu sou alemão.
- She is Brazilian and I am German.
- Somos espanhóis.
- We are Spanish.
The mistake to avoid
It is do Brasil but simply de Portugal - the article belongs to the country name, not to the rule.
Where this fits in
Greetings & introductions, Portuguese A1: Say hello, give your name, ask someone else's, and where they're from. European Portuguese.