Link building is one of the foundations of search engine optimisation. While search engines are constantly adjusting their algorithms to provide their users with the most relevant results, the requirement for high quality links has remained unchanged over the decades. If you want to build a healthy SEO campaign, you will need to understand what link building is and why you should implement it.

Fundamentals of link building
Link building is generating a library of links on other websites that point to your website. When search engines crawl the Internet to build their search results, they look at the links between individual pages on your website and between other websites and your site.

While most search engine optimizers agree that it is important to build a high-quality link portfolio, they also agree that it is difficult. Waiting for these links to develop organically can take years-even decades. You can pay low-quality sites to place your link on one of their pages, but if their relevance to your website's content is low or their own ranking in search engines is low, you run the risk of your ranking plummeting.

Understanding Hyperlinks
To understand why it is necessary to build links, it is necessary to understand how links are built and how web crawlers read and interpret links. A link consists of four sections: the start tag, the link reference (the URL), the link text and the end tag.

Start tag - In HTML, this is an anchor. You will see it denoted by an "a". When a search engine scans a site, this is the tag it uses to identify a link.
Referral - The next piece of HTML you'll see is "href". This is the hyperlink reference abbreviation and is paired with the URL you want to target.

Link Text - This is the piece of text that viewers of the website will actually see when they are on the page and can click on it to follow the link.
End tag - This closes the link.

Why search engines care about links

Links are one of the many factors used by search engines to determine the relevance and quality of a particular page they are indexing. While relevant content and keywords will always be vitally important to a page's ranking, the number of external links pointing to a particular website shows a web crawler that that site is likely to be filled with good content that others found relevant and of sufficient high quality to list as a resource.

In the past, you could simply submit your website to a directory and get a high quality link in return. Now Google advises against this practice and will, in fact, penalize a website that is listed in an online directory. Fortunately, there are still many legitimate link building tactics that an optimizer can use to improve page rankings.

There has been speculation that updates to Google's algorithm have reduced the importance of links in favor of social cues (specifically to encourage the use of Google+). However, the shutdown of Google+ and the reduction in the traditional social media user base over the past three years has led many optimizers to speculate that links are once again the most important factor that web crawlers consider in page rankings.

Nofollow Links

Not all bonds are created equally. If you look at the code behind a link, you may see a "nofollow" tag included in the HTML. This tag is a signal to web crawlers to ignore that link. This tag is commonly used on websites where users can post links (for example, in a forum or in the comments of a blog), to prevent the hosting website from having to moderate those links.

Posting your link on a website that uses nofollow tags in its links will not improve its ranking on the page. Here are some of the most common places where nofollow links are implemented

Signing of guest blog entries

Wikis-The Yahoo!
Feedback service for blog entries
Forums (including Reddit, until the mail receives a terminal number of positive votes)
Guestbook messages.

Most web crawlers also prefer that links included in any type of paid advertising be labeled as nofollow, as this prevents their organic search ranking from being inflated.

Source: Hispanolinks.com

Author's Bio: 

Leonardo Suárez