follow and nofollow link
SEO for dofollow and nofollow
nofollow tell to the search engine to don't follow links on this page and follow tell to the search engine to follow links on this page.
nofollow
Nofollow provides a way for webmasters to tell search engines "Don't follow links on this page" or "Don't follow this specific link.
Nofollow links attributes do not allow search engine bots to follow link. Only Humans will be able to follow the links. That means if the website owner is linking back to you with nofollow attributes, it does not pass on link juice. Always use nofollow link attribute to those link, where you don't want to pass link-juice.
nofollow
<a href="http://www.google.com/" rel="nofollow">Google</a>
dofollow
Dofollow links allow google (all search engines) to follow them and reach our website. Giving us link juice and a backlink. If a webmaster is linking back to you with this link both Search Engine and Humans will be able to follow you. The best way to give someone dofollow love is allowing keyword in the anchor text. This means when you are linking to any website or page, use the targeted keyword as anchor text.
Example of dofollow
<a href="http://www.google.com/" rel="follow">Google</a>
OR
<a href="http://www.google.com/" rel="follow">Google</a>
Note: By default all the hyperlinks are dofollow. So, you don't need to do anything to make a link do-follow.
Types Of No-Follow
follow links on the full page
Robots Meta Tag : <meta name="robots" content="nofollow"/>
This tells bots/crawlers/spiders not to follow links on the full page.
Example
Link Attribute : <a href="http://www.google.com" rel="nofollow">
This tells search engines not to count the link in terms of ranking pages.