So, how people know about your website?? Broadly it can be classified into 3 categories:
2.Online Marketing
3.Offline Marketing

Online Marketing is paid marketing like SEM. You pay the search engines to show your AD in their web search results.

Offline marketing is through word of mouth or print ADs, which is totally ineffective.

SEO, is Search Engine Optimisation where your website is optimised to show on top of the search results, which can be a major source of Web Traffic. Basically your website’s ranking is increased with the search engine which will make you on top of the search results.