Portuguese - Seu and Sua - Also the use of Perfect and imperfect past tenses

Hi all

Two questions:

First:

Seu and sua mean your, her, and his in both portugal portuguese and brazilian portuguese. Is that correct?

Second:

The usage of perfect past tense and imperfect past tense confuses me a lot. For example,

When to use: Eu estive muito feliz

and: Eu estava muito feliz

Is the usage of these two sentences correct?

Thanks in advance

Sarah