AT THE END vs IN THE END

At the end v/s In the end

At the end means ‘time when something ends’.

--- At the end of the day
--- At the end of the week
--- At the end of the month
--- At the end of the semester/year/course
Examples:
1. It becomes extremely difficult to satisfy the demand of all customers at the end of the month.
2. The players hugged each other at the end of the game.
3. At the end of the party, we exchanged our mobile number.

In the end means ‘finally’.

Examples:
1. In the end, she got visa for Australia.
2. Brazil played very well and in the end they won the crucial match.
3. Doctors tried their best to save the patient. In the end, they saved him successfully.