SEO means Search Engine Optimization i.e. optimizing your website as per the guidelines of search engine. A Google has more than 78% of market share of entire search engine space. So most of the business owners are optimizing their website to reach on the top positions in SERP's (Search Engine Result Pages). SEO results are also known as organic search or natural search; that means you do not have to pay someone to get ranked on Google. All you need to learn and implement ON-page & Off page techniques on your website and you are good to go to get leads and customers for your business.
SEO is important because it is available and results can be seen 365x24x7. SEO results are more genuine, trustworthy and help customer to take better buying decisions.