What is the "books received" section in journals? Is it the books that will be reviewed later on, or the ones that were not reviewed? Who can send their books to the "books received" section, and what's the point of it?
It is what it says on the tin: a list of books that the journal has received copies of. The review editor(s) can then pick interesting titles from this list, and send them out for review for a future issue. Space is usually limited, so typically some of the books won't be reviewed in the journal. The journal might also decline publishing some completed reviews. For those cases, the list serves as recognition "of the courtesy of the sender".
As far as I know, usually anyone can send their books to the journal - be it a publisher, an author, or a reader who just happens to have a spare copy. Readers can also notify the journal about a certain book that they would like to see reviewed, or volunteer to review one, whether it has shown up on the list or not. Presumably, if readers of the journal are interested in the book, the journal would be more interested in publishing a review.