Most pre-published authors mistakenly believe that their publisher will handle all their marketing needs when they finally sell their first book--especially if they're seeking a traditional publisher. While a publisher will help, most likely your book will appear in long lists with other new books printed in the same week or month as yours. Authors with a proven history of sales and great print-runs will receive the bold listings, call-out features, highlights, store displays, aisle displays and cover racks. New authors are blessed to be on the shelf.
Promoting and marketing your books will be YOUR responsibility as the author. All the years you spend polishing your writing and promoting your work to agents and editors is a test of preparation. It prepares you for the real thing--promoting and selling to the public. This is hard for writers as 80% of us have introverted personalities. We dislike being in the spotlight. We just want our writing to shine and make a difference in the lives of others. That's fine, but in order to make that difference, your writing has to produce sales so your editor can justify why they need to keep publishing your work. Without publication, people won't experience the benefit of your work.
Yes. Yes. Yes.
You don't have to spend a lot of money on a professional website with all the bells and whistles with the latest flash craze, nor do you need to learn a lot of html hand codes. Start out with a simple blog through Blogger or Wordpress. They are free or you can buy a domain name for $10/year on Blogger and secure your domain name. Blogs now have static pages on them that function like a website. The bottom line is to create your special place on the Web that tells agents and editors all about YOU as an author. One of the first places they will go to learn more about you after reviewing a proposal is the Web. You can't make a great impression if you don't have anything for them to view.