Talvez seja: "Meu nome é.......... (Marcos)" Maybe it is: "My name is.............."

like Lalli said, I guess the most used sentence in portuguese is "Como você está?" ... which also means "how are you?"... the answer for this question can be: "Estou bem." - I'm fine. "Não tão bem." - Not so good. "Estou ótimo." - I'm great

I dont know if there is amost used phrase, but I think if there was it would be "Oi, tudo bem?", wich means, hello, how are you?. Everybody says that at least once a day.