Social bookmarking can expose your website to thousands of people for free. Besides that, you can get some backlinks as niessuh noted.
Social bookmaring sites are sites that let you post your favorite site so others can see them. It cabn be website or just post on a blog. They can drive alot of traffic to your site and some are do follow
some good points about social bookmarking, but the problem with it in my opinion is that you continually have to keep posting your links for them to have any effect. Personally I'd stick with blogging or high quality link exchanges with other sites that are similar to yours.
which links u like and want to book mark it on social book marking websites. Generally people can do submit their own website for social book marking.