The biggest difference between search engine marketing (covered here) and search engine advertising (covered earlier) is that search engine marketing is free (score!).
Search engine advertising is a great deal, but it's hard to beat free. Remember earlier when we mentioned the results of a search being shown and then the "Sponsored (i.e.: paid) results" shown as well - well, it's possible to be included in the regular/free results by optimizing your site for the keywords you're targeting.
What is "Search engine optimization"? It's basically a list of things you do to your web site to let the search engines know what you're all about. It involves everything from the domain name you choose, to the title of your pages, to your headers, meta tags, and the description of your web site, and - most importantly - the content on your web site. It's almost impossible to get high search engine rankings without good content. Even retails sites (as opposed to content sites) need good content if they want to rank well on SERPs (search engine results page).
There are a whole host of things you'll need to do to rank high in the search engines if you want to do it yourself. But there is another alternative to learning and doing this yourself (though learning and doing search engine optimization yourself is definitely the cheaper route).
There are companies out there, lots of them actually, that will professionally optimize your site for you. One small site I had only cost $130 to optimize (2 hours of work x $65 an hour) another site I work with has cost over $5,000 to have optimized (it's a big site). Since you're just starting out, you can probably have your site optimized for closer to $130 than $5,000.
Was it worth the $130? I definitely think so. Before the optimization, my site was only ranked for one keyword on three search engines. Afterward it was ranked for a half dozen words across the top 10 search engines. In the end, it was probably the best $130 I've ever spent for my site.
So, if I get 5,000 visitors this year due to my optimization that works out to only 2.6 cents per visitor. A great deal considering they were searching for exactly what my site has to offer.