Keep it Simple, Past Simple

A common mistake of non-native English speakers is to use the past simple forms of the verb be (was/were) with infinitive or past simple verbs.

For example, you canNOT say:

I was went to the cinema yesterday.

I wasn’t go to the cinema yesterday.

Were you go to the cinema yesterday.

But you can say:

I went to the cinema yesterday.

I didn't go to the cinema yesterday.

Did you go to the cinema yesterday?

Yes, I did. / No, I didn't.

As you can see in the examples above, the past simple tense is reflected in the main verb in affirmative phrases, or in the auxiliary verb did in negative phrases, questions and short answers. In negations and questions the auxiliary verb is accompanied by the infinitive form of the main verb.

So when can we use the verb be in the past simple? 
We can use be with…

an adjective: The movie was horrible.

a (pro)noun: She was an actress.

a gerund in the past continuous tense:

I was watching a movie, when the phone rang.

a past participle in the passive voice:

The film was directed by Almodovar.