What is Dofollow Commenting and know dofollow sites

Dofollow commenting means commenting and leaving a link of your blog in a site that offers a dofollow link. If you are leaving a backlink through comment in context for SEO then you must first know that the link you comment on must be dofollow.

What Does Dofollow and Nofollow mean

Dofollow means that Google provides you advantage when you link to someone's blog or site. If you link in a site which has nofollow relation in the link then you get no advantage in context of search Engine Optimisation.
Dofollow means search eagine will crawl your link where as nofollow means it doesnot.

How to know a site's Link is Dofollow or Nofollow

It is very easy to know if a siteis ddofollow or nofollow and if you are benefited when you leave a link or not. Simply in the blog post view the page source of the page(In chrome Right click and View page source). Then if you find in hyperlinks rel="nofollow" attribute then there is no use of leaving comments while by default the links are dofollow.