Past Simple is formed by using the 2nd form of irregular verbs or ending -ed for regular verbs.
For example:
I did it yesterday.
They did it yesterday.
He came yesterday.
I did not do it yesterday. (= didn’t)
They did not do it yesterday. (= didn’t)
He did not come yesterday. (= didn’t)
Did I do it yesterday?
Did they do it yesterday?
Did he come yesterday?
Cases of using:
1. Past actions which happened one after the other
She sealed the letter, put a stamp on it and posted it.
2. Past habit or state
He used to go/went to school on foot.
3. Complete action or event which happened at a stated past time
She called an hour ago. (When? An hour ago.)
4. Action which happened at a definite past time although the time is not mentioned. (This action is not connected with the present.)
Shakespeare wrote a lot of plays. (Shakespeare is now dead; he won’t write again. — period of time now finished)
Time expressions used with:
yesterday, last year, last month, last week, long ago, when, in 1967 etc.