The boy read a book.

Meaning: This means that the young male person looked at and understood the words in the book. It's like saying, The young male person looked at and understood the words in the book.

Choice of Words: The boy refers to a young male person, read is an action that means to look at and understand written or printed words, and book is a collection of written or printed pages that tells a story or gives information. When you put them together, "The boy read a book" means that the young male person looked at and understood the words in the book.