Linking is the important part of Search Engine Optimization, either your linked to another site or your being linked by another site. Links in your blog or content, by default are dofollow. If its tagged with rel = nofollow, then it is nofollow link. The difference between them is explained below: If site with high DA or PA is linked with you, google increase your authority for dofollow links. But if it has used nofollow tag then google wont increase your authority.
Nofollow links attributes do not allow search engine bots to follow link. That means if the website owner is linking back to you with no-follow attributes, it does not pass on link juice.
Dofollow links allow google (all search engines) to follow them and reach our website. Giving us link juice and a backlink.