Link building is an important aspect of search engine optimisation. The quantity and quality of inbound links pointing to a website has a major influence on its Google Page Rank number . Page Rank (PR) is an approximated value used to determine the relative importance of your website content on the web as a whole. This page rank number will affect your search engine placements.
In short more and better links will give a higher page rank (PR) value, leading to better search results.
Link building opens avenues through related websites and directories that help bring in more visitors who otherwise might not have found your website or be aware of your services.
There are many ways to attract related websites to link to your website, these include direct link request through email, internal linking throughout you own site, links offered to reviews, directory links, blogs, great content, reciprocal linking, inbound links and more...