dofollow means is a plain HTML link that indicates to users that text is hyperlinked. It also tells search-engine spiders to crawl your link. <a href="http://example.com">Your Anchor Text</a>
When you go for the nofollow it means <a href="http://www.example.com" rel="nofollow">Your Anchor Text</a> It exact means is Spiders won't follow the link,Users may still click & follow the link,Page Rank is not transferred,Anchor text is not transferred to your link profile.