Link building points to establishing relevant, inbound links to your website which help your website achieve higher ranking with the major search engines and drive targeted traffic to your site.

Link building is very important for a site or blog.It increases the ranking of a site.Getting backlink from other site and making inbond links are called link building.

Search engine while deciding the rank of web page in search results take multiple things into consideration. And the most important of that is the number of inbound links to your page. If you have more number of links linking to your website then its likely that your pages will rank higher.

So link building is an activity where webmasters try and build those incoming links. There are multiple techniques of link building some of which are listed below

1. Buying links
2. Affiliation with other websites
3. Social tagging and bookmarking
4. Commenting on blog posts and forums

Hope this is useful

Getting links from other websites or linking own website

Link Building is most of the most important part of the SEO. Link Building we can also call it all Off Page Techniques of SEO
1. Bookmarking
2. Article Submission
3. Directory Submission
4. Blog Submission
6. RSS Submission
7. Classified Posting
8. Press Release
9. Forum Posting
10. Answer Site Posting
11. Social Media Marketing
12.Guest blogging
13.link diversification
14.info graphic submission

It is also help to create good quality backlinks