Firstly lets just define the difference between a natural search and Sponsored Search.
Natural search is the process where search engines send a robot (also called a spider) to your site. A Robot is simply an automated program that catalogues content on your site and decides what your site is about. The search engine then places your site in the search results where it feels you best fit in. How popular your site is also plays a major part in where in the search results your site features. There is no charge to appear in Google's Natural Search.
Sponsored search is the process where you bid on a particular keyword/s. If you were selling DVD's about marketing online, you might bid on a keyword such as “Marketing DVD's”.
The best way to get Google to locate your site is to get other websites to link to yours. As Google “crawls” through the web, it will find your site and catalogue it.
The more links (and the more relevant the links are) the quicker Google will find your site and add it to its index. Read here how to build links to your website. Also, the more links there are to your site the more popular your site will look to Google and the higher page rank you will receive (read Trent's top 5 tips to getting ranked in Search Engines).
Your site can take up to 3 months to appear in Google's natural search and the faster you build links to your site the faster this process will occur. This can be quite a long wait for some businesses and sponsored campaigns are a quick way (within 24 hours) to get into Google.
