to be: SER (as in "I am a boy - eu sou um rapaz) this verb indicates something permanent Present simple conjugation:

Eu Sou

Tu És

Ele/Ela É

Nós Somos

Vós Sois

Eles/Elas São

to be: ESTAR (as in "I am at the cinema" - eu estou no cinema) this verb indicates something temporary Present simple conjugation:

Eu estou

Tu estás

Ele/Ela está

Nós estamos

Vós estais

Eles/Elas estão

Note that vós is no longer in use by any Portuguese speakers. Tu is used only in Portugal between very close family members, or friends. Portuguese still uses the future subjunctive tense, unique amongst other Romance languages.