You already have one past tense, the pretérito perfeito, for things that happened and were over: Ontem eu comi um pastel. Portuguese has a second one, the pretérito imperfeito — the past of things that used to happen, again and again, or that went on for a while:

• Quando eu era criança, eu brincava na rua. — When I was a child, I used to play in the street.
• Aos domingos, a gente comia na casa da vovó. — On Sundays, we'd eat at Grandma's.
• Naquela época, ela morava em São Paulo. — At that time, she lived in São Paulo.

English has three ways of describing a habit like this — I used to play, I would play, or a plain I played — and Portuguese uses this one tense for all three.

Two new words: brincar is to play for fun — games, toys, make-believe (sports take jogar). And era is ser in this tense: quando eu era criança — when I was a child.