Ser indicates a permanent state of being - he is a doctor - ele é medico. He was a doctor - ele foi médico Estar indicates a temporary state of being - she is in the kitchen - ela está na cozinha. She was in the kitchen earlier today - ela estava na cozinha mais cedo hoje.

Hello! There are 3 articles here in Italki that discuss about theses topics. I hope they are useful: >> VERBOS SER e ESTAR: https://www.italki.com/article/377/Differences-Between-Ser-And-Estar-In-Portuguese https://www.italki.com/article/352/To-Be-Or-To-Be%3F-Using-Ser-vs-Estar-In-Portuguese >> PAST TENSES https://www.italki.com/article/718/Eu-tinha%3F-Eu-tive%3F:-How-To-Use-Past-Tenses-In-Portuguese

You can use this site to conjugate: http://www.conjuga-me.net/ and this article explain the differences: https://www.italki.com/article/352/To-Be-Or-To-Be%3F-Using-Ser-vs-Estar-In-Portuguese

Estar refers to the state, denotes something temporary and Ser refers to something permanent, for example: Eu estou feliz = In this moment I'm happy. Eu sou feliz = I am a happy person every time. In the past: Eu estava feliz = In that moment of the past I was happy. Eu fui feliz = In the past I was happy.