The first ten seconds
Introductions in Portugal follow a script. Not a rigid one, but consistent enough that departing from it registers, and the parts that go wrong for foreigners are rarely the words.
Four stages: the greeting, your name, the physical bit, and the phrase that closes it off. The physical bit is the one people worry about, and with some justification.
1. Greet by the clock
English has "hello" for all occasions. Portuguese wants to know what time it is.
- Bom dia, from waking until around one in the afternoon.
- Boa tarde, from roughly one until dark. The switch is tied to lunch rather than to noon, which catches people out, and bom dia at quarter past one gets you a small correction.
- Boa noite, after dark, and it works for both arriving and leaving. Also used walking into a dim restaurant at six in summer.
Olá exists and is fine with friends. With someone older, someone senior, or anyone in a professional setting, lead with the time-of-day greeting. It costs nothing and it is never wrong.
2. Chamo-me, not me chamo
Portuguese says your name with a reflexive verb, chamar-se, to call oneself. Where you put the pronoun announces which country's materials you studied with.
Portugal: Chamo-me [name].
Brazil: Me chamo [name].
The second one is not a small regional preference here. Opening a sentence with me reads as plainly ungrammatical in Lisbon. Learn chamo-me as a single unit, one sound rather than two words, and you will never have to think about it again.