What is the difference between Search Engine Marketing (SEM) and Search Engine Optimization (SEO)? The difference is in how do you get visibility and traffic for your website? There are various approaches, but two basic ones exist –Paid Ads and Organic Placement.
Paid Advertisements
Paid advertisements provide immediate placement. You simply create a title and blurb based based on keywords that relate to your site. When you submit your advertisement, it immediately shows. This is an effective way to get visibility and traffic. The process is simple and straightforward.

Should you use paid advertisements, careful choices in keywords/phrases will bring you traffic. Failure to research the terms will only result in costly clickthroughs with little or no Return on Investment.

Organic Optimization
Organic optimization requires technical skills and content-oriented websites. Paid advertisements have nothing to do with your website. Organic optimization is all about content, coding and linking. While organic is more difficult, it provides greater click throughs and gives your website more credibility.

Studies show that searchers click through organically placed results than they do paid advertisements. Here are a few reasons:

1) Being in the top few positions brings a credibility factor to your website. People search for websites that match their searching criteria. They look specifically for the top positions.

2) People have learned that paid advertisments are just that—advertisements.

3) Eye tracking studies show that both new and experienced computer users heavily focus attention on the top placements rather than the paid advertisements.

Organic optimization is the best of the two. There are times when you should use Paid Advertisements, but they should only be used when you need immediate placement or the competitveness of your industry demands continual paid advertisements.