No followed links are links that don't carry any 'link juice'. A lot of websites like twitter and facebook as well as comments on websites have no follow links because they don't want people spamming them to get easy links.
Root domains are like www.seomoz.org or www.cnn.com. So if you have 300 links and 30 linking root domains that means that 30 different sites are linking to you.
This is From The SEO Moz SEO Guide. (It's under chapter 4)
" Rel="nofollow" can be used with the following syntax:
Links can have lots of attributes applied to them, but the engines ignore nearly all of these, with the important exception of the rel="nofollow" tag. In the example above, by adding the rel=nofollow attribute to the link tag, we've told the search engines that we, the site owners, do not want this link to be interpreted as the normal, "editorial vote."
Nofollow, taken literally, instructs search engines to not follow a link (although some do.) The nofollow tag came about as a method to help stop automated blog comment, guest book, and link injection spam (read more about the launch here), but has morphed over time into a way of telling the engines to discount any link value that would ordinarily be passed. Links tagged with nofollow are interpreted slightly differently by each of the engines, but it is clear they do not passas much weight as normal "followed" links
Are nofollow Links Bad?
Although they don't pass as much value as their followed cousins, nofollowed links are a natural part of a diverse link profile. A website with lots of inbound links will accumulate many nofollowed links, and this isn't a bad thing. In fact, SEOmoz's Ranking Factors showed that high ranking sites tended to have a higher percentage of inbound nofollowed links than lower ranking sites."
As far as how to fix it, when you have no followed links that generally because that is the way the website has the structure setup and there isn't anything that you can do about it. If you have a lot of links and not many linking root domains, you just have to try to diversify your links through link building.