Layout design is arranging the information and graphics in a publication or piece to make sure it is easy to read and flows well, in addition to making sure it looks good.
Layout design takes kerning, leading, font choice, spacing, widows and orphans, rivers, gutters, margins, bleed, page count, and more into consideration.
You should absolutely judge a book by it's cover! A good cover design catches a reader's attention while representing the central message of the book.
For paperback books this means creating the front and back cover and spine. For hardback books this also involves deciding on the design for the interior boards, the cloth binding, and the jacket if there is one.