Dofollow is a term of Indication by which Search Engine spider can pass the juice of a site to the other sites which are linked with it. When we put an anchor text to a website and if we do not make it ‘Nofollow‘, Then is a Dofollow Link, And when search engine spider/crawler come to that site and found a link which is Dofollow then It will provide some juice to the site which is linked.
Look At the Picture
In Practical, If we have a website or blog as an example blog A. (rakeshsardar.com) and I anchored a text and hyperlink it with some other website or blog as an example blog B. (nowthisdigital.com) and make is Dofollow. Then the SEO juice will pass through blog A to blog B, that means rakeshsardar.com to nowthisdigital.com.
Now if you look at the page source of this post(In chrome press ctrl+u), then you may see on the hyperlink of the text ‘nowthisdigital.com’ is getting a dofollow link from this site (rakeshsardar.com).