This is the 185th most frequent Ukrainian word.
стати
"Stati" (стати) means "to become" or "to stand" depending on context.
In this sentence, 'стати' is used to mean 'to become', indicating a change or adoption of a new status or role.
Я хочу стати лікарем.
I want to become a doctor.
Here, 'стати' describes the action of a subject (the book) achieving a certain status or condition (becoming a bestseller).
Ця книга стала бестселером.
This book became a bestseller.
In this context, 'стати' is used to describe physically positioning or placing oneself (to step onto).