。
Yumi has a lot of books.
Literal
Yumi [topic-は] books [object-を] many have-[ongoing-ている].
持っている ('has') — literally 'is in the state of holding' — is the possession form. 持つ means 'to hold, carry' in its plain form, but as a possession verb it's always in ~ている. A classic intro-level sentence.