Dofollow Link is the links that benefit your website when you receive it from another website, and when you give it to another site from your own site. You do not need to create a rel tag for Dofollow links. The links you provide are perceived by the robots as dofollow.
Google takes into account the content on the sites to determine the quality of a connection. When the links from other sites come to your site as a doofollow link and these sites have content related to your site, these incoming links are considered to be more relevant to your site. Incoming connections are considered less relevant if they are found on sites with indifferent content. As the relevance of the incoming connections increases, the quality increases.