Your life as an author doesn't end with the contract. You will receive a note from the publisher with the Dreaded Art sheet. This concerns your cover and asks questions about your idea about what should be on the cover. To those who are visually focused this sheet can be a breeze.
The artist who will design your cover wants a description of the main characters, the setting and perhaps a scene you want to focus. Other material is also wanted like your blurb. This is a short. very short, idea of what your book is about. One way to do this is to take the two main characters and show their wants and their way of obtaining their goals. This isn't easy and sometimes seems to take as long as the book to write. Done well this will have a reader on fire to read your book. These are short, concise and tempting. I once even sold a book on a very short blurb and little else.
The publisher may also want a short bio for the book included.
Some publishers give you a lot of leeway on the cover and others don't. Just fill our the sheet as best as you can.