Dofollow and Nofollow links are another concept of link building
They are used to create reputation by linking your website to another website with more traffic. This way you can improve your website rank in SERP. By default all links are dofollow as there is no need to define it within the anchor tag but some website requires approval from moderators to backlink.
'a href="#" rel="dofollow">text /a'
when you want to link a website that ranks lower than yours then Nofollow property can be used.
I have used nofollow link to one of my posts here in Hungryforhits to show it only as an example and i want you to click the link and join :)
Use these links in blogs to refer a website for explanations.