The Imperfect Storytelling Tense
The Simple Past tense gives you the skeleton of a story. This happened, then that happened. But the Imperfect tense (Pretérito Imperfeito) adds the flesh and blood. It builds the atmosphere.
It's the difference between listing facts for a police report and telling a story to a friend over uma cerveja.
This tense tripped me up for ages. English doesn't have a perfect match for it. Sometimes it translates to "I used to," sometimes "I was doing," and sometimes just "was." It felt slippery.
(Note: If you are specifically stuck on the confusion between was and was—like Era vs. Foi—start...