Nowadays, over 95% of people rely on internet in order to get product or service information.
And, most internet users concentrate on first three pages of Search Engine Results Pages (SERP).
When searching for a product or service in search engine, users are more likely to choose one of the top three suggestions (top three pages). Without good SEO, your website will not be found in these suggestions (pages).
Users trust search engines and having a presence in the top positions for the keywords the user is searching, increases the website's trust.
SEO can put you ahead of the competition. If two websites are selling the same thing, the search engine optimized website is more likely to have more customers and make more sales.
if potential customers can’t find your website, sales opportunities are being missed. SEO increases your organic search engine traffic, in turn increasing the number of visitors your page sees each day. This directly correlates to an increase in sales – because the more relevant people that see your site, the more likely you are to sell to them.
SEO is one of the most cost-effective forms of digital marketing. Once you start ranking well for terms, you receive the benefit of consistent traffic that the particular search term provides each and every month, so your flow of potential customers continues. Very few marketing channels can say the same thing.
Paid search engine advertising (PPC) and SEO work well together. Website rankings at the top of paid search results and among first-page organic rankings provide consumers additional opportunities to visit your website and bolster brand credibility. Additionally, SEO data can be utilized to inform and optimize your PPC strategy.
SEO techniques can be classified into two broad categories: techniques that search engine companies recommend as part of good design ("white hat"), and those techniques of which search engines do not approve ("black hat"). The search engines attempt to minimize the effect of the latter, among them spamdexing. Industry commentators have classified these methods, and the practitioners who employ them, as either white hat SEO, or black hat SEO. White hats tend to produce results that last a long time, whereas black hats anticipate that their sites may eventually be banned either temporarily or permanently once the search engines discover what they are doing.
An SEO technique is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines are not written as a series of rules or commandments, this is an important distinction to note. White hat SEO is not just about following guidelines but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see. White hat advice is generally summed up as creating content for users, not for search engines, and then making that content easily accessible to the online "spider" algorithms, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is in many ways similar to web development that promotes accessibility, although the two are not identical.
Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines, or involve deception. One black hat technique uses hidden text, either as text colored similar to the background, in an invisible div, or positioned off screen. Another method gives a different page depending on whether the page is being requested by a human visitor or a search engine, a technique known as cloaking. Another category sometimes used is grey hat SEO. This is in between black hat and white hat approaches, where the methods employed avoid the site being penalized but do not act in producing the best content for users. Grey hat SEO is entirely focused on improving search engine rankings.
Search engines may penalize sites they discover using black or grey hat methods, either by reducing their rankings or eliminating their listings from their databases altogether. Such penalties can be applied either automatically by the search engines' algorithms, or by a manual site review. One example was the February 2006 Google removal of both BMW Germany and Ricoh Germany for use of deceptive practices. Both companies, however, quickly apologized, fixed the offending pages, and were restored to Google's search engine results page.
Reference: https://en.wikipedia.org/wiki/Search_engine_optimization