Building backlinks, either organically or paid, is extremely important to ensure that your website ranks highly for particular search terms and drives traffic to your website. They are the key factor for successful search engine optimization (SEO), so their importance should never be underestimated.
These (also known as "inbound" links) are links on other websites that point towards your site. They are gained by other webmasters manually adding your website's link on their website, or can be purchased for a predetermined monthly fee. The cost of a link is based on the website's popularity, Google PageRank, Alexa rank and various other factors.

The quality of a link must also be taken into consideration. One that is placed on a website that is properly designed, is optimized for search engines and has content relating to your own is considered far superior than a link on an irrelevant and unpopular website.

While it is best to build as many links as possible, it's important to remember that it is much better to have two quality links than twenty low-quality links. Google (and other major search engines) will penalize your website if it is noticed that there are too many "junk" links, ultimately resulting in your website being pushed down in the search engine ranks. If you are caught to have purchased a number of links, Google will further penalize your website by either completely removing it from their listings or placing you into their "sandbox".

The safest method to gain organic backlinks is to create quality content for your website. These naturally gained links are usually the highest quality and do wonders for your overall rankings.