The word "ago" is an adverb that is used with the past tense. When we say something happened a time ago, the comparison is between now and that past time. The word "ago" often appears at the end of a sentence or a clause but not always.
She was born 42 years ago in Egypt.
He moved to New York ten years ago.
The accident happened a few weeks ago.
Five years ago, Marta and Jose moved to Chicago.
Over 30 years ago I began my career as a teacher.
Rome was a powerful city state two thousand years ago.
Planet Earth formed 4.5 billion years ago.
That was a long time ago.
I operated a conference bike business
in Minneapolis over ten years ago.
To indicate a relatively long passage of time, make a plural of a unit of time, such as days, weeks, years, and then use the word "ago."
The plane left hours ago.
He turned in his assignment days ago.
They moved away months ago.
The last time I saw her was years ago.
That was weeks ago.
That was ages ago. (ages = a long time)
That happened some years ago. (some years = three to ten years–very indefinite)
When forming questions, the word "ago" can go at the end of the question or after the words "how long."
Where did you live five years ago?
How long ago did you live in China?
What were you doing twenty years ago?
How long ago were you a student?
How long ago did you attend school?
How many years ago did they get married?
How many years ago did you start learning English?
This video provides additional instruction for the word "ago."