This is the 15734th most frequent Russian word.
приходятся
"Приходятся" means "are/turn out to be" or "fall to" depending on context.
In this sentence, 'приходятся' is used in a colloquial context to indicate that the books are suitable or useful at the current time.
Эти книги мне очень приходятся кстати.
These books are very timely for me.
Here, 'приходятся' is used to describe an occurrence or allocation related to responsibility or experience.
На долю детей приходятся самые трудные времена.
The hardest times fall on the children.
This usage of 'приходятся' shows a relational association or kinship.