Difference is due to the usage of prepositions:
1) At the end:
Example: I can see light at the end of the tunnel.
Example: The restrooms are at the end of the hall.
2) In the end:
Example: The hero killed the villian in the end.
Example: I laughed so much that I cried in the end.
3) To the end:
Example: I will go to the end of the world for you.
Example: I will make you read to the end of the story.
4) By the end:
Example: I want the reports by the end of day today.
Example: Catch it by the end of its tail.
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