new book; unused book
Refers to a book that is physically new or unused, as opposed to a secondhand book.
This book is new, so it doesn't have a single scratch.
newly-published book
Refers to a book that has just been published, emphasizing its recent release rather than its physical condition.
It seems that author's new book will be released next month.
新本 means a brand-new book, the direct opposite of 古本, a previously owned or secondhand one.
Compound of 新 (new) and 本 (book). The reading しんぽん follows standard on'yomi patterns.