SEO is what will help propel the visability of your site to visitors looking for you.  Unfortunately many people are under the misguided opinion that if you build it they will come.  This is probably the greatest myth of the internet.  Just as you would advertise a brick-and-mortar business in the real world you have to have a marketing plan for the internet as well.  The cornerstone of any online marketing campaign is an active SEO campaign.