The nofollow attribute is the signal webmaster’s concern to the search engines to let them know they want to treat a particular link a little differently.
A normal follow link from one website to another is a kind of endorsement. Followed links can crawl and indexed by the search engines as they pass from one page to another. They also pass link equity to the destination page and contribute to the destination page’s page authority as well as destination website’s domain authority.
A nofollow link is in quite endorsement. When a search engines comes across a nofollow link from one page to another, they won’t index the page on the far side of that link with the destination page. A nofollow link does not pass any link equity and it won’t contribute to the destination page’s PA or the destination website’s DA. In order to turn a follow link into a nofollow link, the webmaster adds the small code attribute which you can in the bold text on the right to the code for that particular link in HTML. You can have both follow and nofollow links on the same web page, whether each link is followed of no-followed just depends on the presence of this little piece of code.