No follow links don't allow search engine bots to follow your links. ... They don't help you to boost Page Rank, website rankings and have no SEO value. It is a notice for search engine not to count a link.
To be clear, they do not stop any bots from following them: they are just a notification to well-behaved bots that these links are not to be considered "quality" links and it's recommended they not be followed and used to give those targets any inbound link credit. What any given bot actually does when it sees that is entirely up to the bot creators (if they even considered it).
Note: all user-submitted links in these forums are "no-follow", for those of you posting here thinking it will gain you more SEO juice.