Nofollow links - Nofollow links attributes do not allow search engine bots to follow a link.That means if the website owner is linking back to you with Nofollow attributes, it does not pass on link juice.
Example of Nofollow Link:
<a href=”http://www.google.com/" rel=”Nofollow”>Google</a>
Dofollow links - Dofollow links allow google (all search engines) to follow them and reach our website. Giving us link juice and a backlink.
Example of Dofollow Link:
<a href=”http://www.google.com/">Google</a>