I read:
Suddenly – boink! -an apple hits him on the head. “Aha!” he shouts, or perhaps, “Eureka!” In a flash he understands that the very same force that brought the apple crashing toward the ground also keeps the moon falling toward the Earth and the Earth falling toward the sun: gravity
Now this story is not litterally true. It is written though that Newton sat in the gardegarden where he spent his his childhood and saw an apple falling. He pondered why apples don't fall sideways but straight down instead.
How did this lead him to his laws? He imagined the apple being the moon that fell (or the moon being the apple). And because of the Earth's curvature it would fall forever, so orbiting. But what is the connection with his universal law of gravitation? Didn't he think before that the same force that makes the apple fall can be applied to the moon, and in fact is the force responsible for the moon's motion. How were the orbits of the planets accounted for before his law? By the planets moving through invisible tubes?