Link building is a key activity for SEO. It can be considered to be an element of online PR since it is about getting your brand visible on third party sites and creating backlinks related to your site.
Link building needs to be structured effort to achieve as many quality links into a website as possible from referring websites (these commonly include reciprocal links which tend to be less valuable from an SEO perspective than one-way links). Your position in search engine results pages will be higher if you have quality links into relevant content on your site (not necessarily the home page).
McGraffic (2004) provides a great introduction to implementing a structured link building programme. The main principle of link building is as follows: ‘create great content, link to great content and great content will link to you’. He describes how you should review existing links, link to competitors, set targets and then proactively enquire to suitable site owners for links.
Reviewing your links into a site
You can use the syntax link:site in Google to see examples of links into a page on a site judged by Google, e.g. site:www.mudu.io. But note that this also includes internal links and is not comprehensive. A better option to display links is the SEOmoz Open Site Explorer tool (www.opensiteexplorer.com). For alerts of new links or new mentions on other sites, Google’s own alerts (www.google.com/alerts) are useful tools.
Chaffey, D. and Ellis-Chadwick, F., 2012. Digital marketing: strategy, implementation and practice (Vol. 5). Harlow: Pearson.