Potential visitors to your website often start by going to one of the major search engines. If they search for something you have, you want them to find a link to your website. This can only happen if the search engines are able to index the pages inside your website.

When search engines index your website, they don't use the same software a normal visitor does. If your website is designed so that JavaScript or frames are needed to navigate the site, then the search engines may not be able to access the internal pages. If important information on your site is stored in a database and referenced with computed queries, the information may not be visible to the search engines.

Proper design of website software can make internal pages and database contents visible to search engines while preserving the user experience.

You can test your website by using the Lynx browser to visit it. Lynx accesses your website in a way that is similar to what search engines do. Any pages not visible using Lynx can probably not be indexed by the search engines.