nofollow and dofollow links have always confused me. Experts say to put nofollow in meta tags to prevent users from spamming. Wikipedia does it! Doing such a thing also helps in your search engine Optimisation (SEO) with your Page Rank not shared with anyone. So how to nofollow link ?
"follow" or as experts call it, "dofollow", simply means that you allow the Search Engines to do what they do best without any issue. So if you put follow in meta tag, it indicates that you are allowing the search engine bots to scrape your content and follow all the links. You can add the dofollow link in the head section of the webpage as a meta tag.
<meta name="robots" content="follow" />What if you do not place such a thing on your website! Well, then the Search bot still believes that you allow them to scrape and follow your website webpage. So placing follow meta tag hardly matters !
Like follow, the nofollow meta tag too needs to be placed in the head section of the webpage.
<meta name="robots" content="nofollow" />This meta tag in the webpage tells the bot that you can scrape the content but do not follow the links of the page. This prevents the bot to follow any link on the page.
For nofollow Google says in Google Webmaster forum
"In general, we don't follow them. This means that Google does not transfer PageRank or anchor text across these links. Essentially, using nofollow causes us to drop the target links from our overall graph of the web."
This was about nofollow, follow and how to nofollow link, but why is it so important and what is this "transfer PageRank" as told by Google ? In very simple terms Google ranks your website page by the number of back-links (other webpages linking to your page) the page receives. This rank gets shared by the number of outward links from your webpage. So your Page rank gets shared to pages you have linked to reducing little of your page rank. That is why there are so many replies and strange comments with other website links in various posts on internet, all getting the Page Rank juice of that page. For better understanding I would suggest you going through a detailed theory at