WERE

where were you? (onde você estava?) interrogative

they weren't there yesterday. (eles não estavam lá ontem) negative

my parents were at the shopping mall. (meus pais estavam no shopping) affirmative

WAS

I wasn't here yesterday. (eu não estava aqui ontem) negative

where was she? (onde ela estava?) interrogative

It was always here. (isso sempre esteve aqui) affirmative