As far as I know you can submit your website's link to several search engines. At least I found this for Google. I don't use other search engines though so I don't know much. Other than that, bots usually crawl through your website to detect content so there's that option too.
Search engines list your website automatically when they crawl and index your website. You can submit your website in webmaster tool to get listed faster.
Search engines work by trying to show the most relevant content for what people search. So naturally, creating content that is informative and catered towards your visitors is the best way to build SEO.
We are already showing up on Googld; however, one must know what to plug in to find us, and no one will know that. That's why I was hoping it could be done via category. The only way I've found to find us on Google's list is by typing KittyPaws + Beehive -- but like I say, someone just looking for a sig forum would not know to do that - sigh.