This is the 80th most frequent Russian word.
свою
"Свою" means "one's own" (feminine, singular, accusative case) in English.
This sentence uses "свою" to indicate the book belongs to the person (he) performing the action, emphasizing ownership in a reflexive manner.
Он нашел свою книгу.
He found his book.
In this case, "свою" specifies that the bag belongs to the person (she) performing the action, showing possession tied to the subject.
Она бережно положила свою сумку на стол.
She carefully placed her bag on the table.
Here, "свою" refers to one’s own point of view, illustrating the use of the word to show a personal and reflexive relationship.