Meaning:

To learn how to do something very easily, quickly, and well when doing it for the first time, especially because of the person's natural ability.

If someone takes to something like a duck to water, he/she finds it very easy to do when he/she learns it for the first time. He/She finds that he/she is good at it naturally.

Example:

Sam is really a natural programmer. He took to programming like a duck to water even before he graduated from elementary school.

A: How's Sandy doing in her new job?
B: Very well. She's taken to it like a duck to water.

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