The past form of BE is was/were.
New York was cold last week.
Miami wasn't cold last week.
Was Washington, DC cold last week? Yes, it was.
Was San Diego cold last week? No, it wasn't.
In this video, Paul explains the past tense of the verb be:
Most English verbs are regular in the past tense. That is, the past form is V + ed.
Example: They work every day. They worked yesterday.
Some verbs are irregular. You must memorize the past tense form.
Example: They go home after class every day. They went home after class yesterday.
All English verbs (except for be) are regular in the negative (did not + V) and question (Did + Subject + V...?).
In this video, Paul explains about be and do (did) in the past tense:
For a more complete review of the formation of the past tense in English, watch this video from JenniferESL:
Here is Part 2 of the lesson:
Part 3 of the lesson reviews past tense forms and question words:
The last part of the lesson talks about questions about the subject (e.g., What happened?) and questions with BE. It also has pronunciation rules for the -ed ending: