Do Follow Links are Considered as a Page Score by The Search Engine, and this kind of links are useful for Website rankings..

There is no actual DoFollow tag. The absence of the NoFollow tag makes the link DoFollow. If a blog or web site doesn't use the NoFollow tag, the search engines acknowledge the link; if a site does use the NoFollow tag, the search engines do not acknowledge the link

Do follow links means google follow the hyperlinks this process called as do follow links.

It is a type of link which has a potential to improve the ranking and the credibility of your website in Google.

It is good for page indexing & PA DA of website

dofollow links also some times be a nofollow links. why?

Check out the links for dofollow before posting.

I think you need to google for this. There are many website available which are promoting content with Dofollow backlink to your website. All you need to provide them High Quality content.