Generally the way people find web sites is through search engines. So it stands to reason you must first get listed in the search engines. Secondly, it will help your message get to the world if you manage to rank highly in the search engine results. That's covered elsewhere, and on this page we're just going to look at getting the first step accomplished.
Reachability
One key attribute is what I call reachability. The more links leading to a page the more likely someone will find that page. A page that has zero links leading to it will not be found at all. If there are no links pointing to a site, then the site is unreachable. It is only when there are links pointing to a site that it is reachable.
This is where Web Directory sites play an important role. It is through getting listed in a directory web site that your site becomes reachable.
I make a distinction between two types of "Search Engine" sites:
- Search Engine: This is the logic behind the "Search" box on some sites. Behind the scenes, the web search engine has visited lots of web sites ("spidered") and copied parts or all of the content. This lets the search engine "index" everything, letting it respond to your "search".
- Directory: This is a topic oriented directory of known sites. For example: dir.yahoo.com
There are many web directory sites, some that cover the whole Internet, and some that cover just a portion. For example, a web directory may focus on a topic and list sites that only fit that topic. Since you don't know which web directory people will use to find you, you want to be listed in them all, probably.
Once you find a web directory you'd like to be listed in, how to do the deed? Unfortunately the process varies from directory to directory. Usually there will be a link marked "Suggest a URL" or something similar, and clicking on that gives you the directions for that site.
For more information look at Promote Your Website - Search Tools
Links from sites other than web directories
Many web sites include links pages. These are pages listing related web sites of interest. Sometimes you can get your site listed on such pages simply by asking the author (via email) to add your site to their list. It's common courtesy to make a reciprocal link from your web site as well.
Search Engines
Search engines work differently than directory sites. Rather than a predefined list of categories, a search engine lets you query against a database of web site content. The difference is what's being searched. In the web directory sites, what's searched is the directory content, while on a search engine what's searched is the content of the web sites.
Assuming you've solved the first problem, making your web site "reachable", the search engine sites will soon learn the content of your site. They do this with a process called "spidering". A search engine site uses special purpose "Spider" software to walk around the web (get it? web? spider?) and gather up everything it finds. It is the web links which spider software follows.
This is why "reachability" is important. If the spider software cannot reach your site, then your site will not be visible in the search engines. So long as there is even just one link to your site, then the search engines will be able to spider your site, and ultimately return pages on your site as a search result. The chain of links can be long and circuitous, but as long as it exists the search engines will know about your site. Of course it helps to have more links to your site, giving the search engines more opportunity to find it.