Ya sabes contar lo que pasó con el simple past: I walked, we went, she bought. Pero a veces no quieres contar una acción terminada, sino lo que estaba pasando en un momento concreto del pasado. Para eso, el inglés usa el past continuous: was / were + verbo en -ing. Es casi un calco de estaba + gerundio:

Pronoun	Past continuous	Español
I	was reading	estaba leyendo
he / she / it	was reading	estaba leyendo
you	were reading	estabas / estabais leyendo
we	were reading	estábamos leyendo
they	were reading	estaban leyendo

• At eight o'clock, I was having dinner. — A las ocho, estaba cenando.
• Marcos and Luana were talking in the kitchen. — Marcos y Luana estaban hablando en la cocina.

Was y were son el pasado de to be (I was tired, we were in London); aquí hacen de auxiliar. Was va con I, he, she, it; were, con you, we, they. Y recuerda: to have dinner es cenar.