Search Engine Optimization (SEO) is simply the process of making your website more accessible to both search engines like Google and search engine users. In other words, you are making it easier for them to find your website/business.
These days, before buying anything, people searches for that product on search engines like Google, to research about that particular products/services. At the very first step, they look for list of sites who provide that particular product/services, so at that time in case if your site is not listed on the 1st page or even at the most on 2nd page of the search results, they will never know your presence in the industry. Instead, your competing websites who have achieved the top rankings on search engines will grab that business!