Learn Italian: È restata in biblioteca. - She stayed in the library.

In Italian, the past tense (passato prossimo) is usually formed with the helper verb avere (to have). However, verbs that describe motion or a state of being—like restare (to stay or remain)—use essere (to be) instead. So, literally, Italians say she is stayed rather than she has stayed.

How do we know this means she stayed since there is no word for she in the sentence?

Two things give it away! First, the verb è tells us the subject is he, she, or it. Second, because we are using essere as our helper verb, the ending of the past action word (the participle) must match the gender of the subject. The -a ending on restata tells us the subject is feminine singular, which means it has to be she. If it were he, the sentence would be È restato in biblioteca.

Why is it just in biblioteca instead of nella biblioteca (in the library)?

In Italian, certain common everyday locations—like rooms of a house, banks, and libraries—do not use the word for the when paired with the preposition in. You simply say in biblioteca, just like you would say in banca (at the bank) or in chiesa (at church).