The carnival host decides on a topic to host a carnival on. Submissions are invited from the public. Webmasters who have blog posts on the topic submit their posts to the carnival host. He then reviews all the submissions and picks a handful that are considered high quality. The host then posts an article with citations from the accepted posts.
A carnival in any niche reflects the pillar blog posts on that niche, or at least that's the idea
So say there is a blog carnival on Niche marketing. Blog owners who have posts on niche marketing can submit there blog posts to the carnival for consideration for inclusion in the carnival
When the blog carnival is published it usually contains a little introduction followed by snippets of the accepted posts with links to the full post at the authors blog
So what does this mean. In a word, backlinks
But are blog carnivals worth investing in to help promote your blog?
Again, in a word, yes. Blog carnivals are very popular and tend to get a ton of traffic when published. Getting one of your blog posts cited in a carnival is like putting your link right under the noses of your targeted visitors.
If your post is decent, a single inclusion could take you from average blogger to super blogger status.
The down side is competition. Getting a blog post accepted in a blog carnival is similar to getting your site into dmoz.
Writing pillar posts that are well thought out with excellent information is a must but unfortunately does not guarantee inclusion
To find out when next a carnival in your niche is scheduled for go to http://blogcarnival.com/bc/