To understand link building, it's important to understand the meaning of common terms used in the process of building links, such as: hyperlink or link is a way for Internet users to navigate between pages on the Internet; "crawl the links" means to move slowly between the individual pages on a website or entire website.
Since link building is considered one of the hardest and complex jobs to do by a SEO provider http://decisiontree.nl/ , a good point of why it is so is to understand the basics of how a link is created, how the search engines put importance on a link, and what the search engines can interpret this importance. The framework of a link is composed of the following: start of link tag, link referral location, visible/anchor text of link, and closure of link tag. An example of a link framework is:
The link begins with an anchor tag, a, which symbolizes the opening of the link tag and conveys a message to search engines that a link representing something is about to follow. Adjacent to the anchor tag, a, are the letters, herf, which stands for hyperlink referral, and there's an opening quotation mark, after href, that indicates the URL (uniform resource locator) - http://www.jinguy.com, to which the link is pointing to the address of an image or to a file to download, and more often there's something other than a URL, beginning with this sign, #, which are referred to as local links which will take you to a different section of the page. After the URL address is the visible/anchor text of link, Jing Uy's Kitchen Soup, which users have to click to open the link. The text is formatted with a blue color or with an underlining to indicate that it is a clickable link. And the last part is the closure of the link tag, /a, which indicates the end of the link tag to the search engine.
Search engines use links for the following reasons: to discover new web pages and to determine how well a page should rank in their results. For the search engine to discover new web pages, it uses a web crawler or spider software to update their web content, extracting the contents of web pages from websites and add them to their indexes. In this manner, the search engine will decide if the crawled page/s has sufficient quality to be ranked well. In the process of deciding, the search engine do not just look at the content of the page, but it also considers the number of Decision Tree links pointing to the page being evaluated, which come from external websites, and the search engine also evaluates the quality of those external websites. The reason for evaluating quality in the websites, whether from the main link or external links, is that the more quality websites that are linked to the main website, the more likely will the main website be able to get a good ranking in the search results.