The reason why people get ads to promote their sites so when you google it or search for it using the many search engines out there, your site is one of the first sites that the one looking for it can click on.  And when you do this well, and you are able to do all the things that you can do to market your site, what you have done is  Search Engine Marketing Optimization.  When you have done this, you can actually make money from your site because that is what marketing does.  It brings money to your company.