Link Building - External or Back link

Link Building:

Link Building/Popularity refers to the number of links pointing to your site from other sites on the Web.
If external websites have a direct link pointing to your website, it is more likely that the popularity of your site will improve. You can start with submitting your site to dmoz.org, Yahoo! and other directories first.
In SEO parlance, external links are also called as Back Links. Back links from reputed sites (that is, sites with a good page rank) could definitely improve the importance of your web page. If the page (from where a back link comes to your page) has been optimized for the keywords relevant to your business, your page will also be rated high by the search engines.
You can also make effective use of forums and blogs to post links to your website popularity. However, keep in mind that many forums do not allow blatant advertising. So, wherever some discussion very relevant to your business is going on, participate in the discussion and then post your link.
To find the number and list of back links pointing your page, you may just do a google search as link: For example, if your website is www.network-monitoring.com, you can find the number of back links as link:network-monitoring.com.