When were you born? When is your anniversary? When was the election?
When we speak about time in English, we have to choose the right prepositions. Here's how we do it when speaking about dates in the past:
Month: in. I was born in October.
Year: in. I was born in 1988.
Day: on. I was born on the 5th. (Or, I was born on Sunday, the 5th).
Put them together and you get ...
The short form: I was born on October 5th.
The longer form: I was born on Monday, May 6th.
The even longer form: I was born on Sunday, June 18, 1977. (We still add "th" to the date, even though we don't write it when using this form. So, this date would be read as "June eighteenth ....")
When did you get here? I got here at 9:00.
When did she leave? She left at 10:00.
When did the party end? It ended at midnight.