Social Bookmarking sites? Visit del.icio.us, stumbleupon and similar websites to know how they work. They all have pretty much same working. If you mean to get backlinks from other websites, you can exchange links with other people or simply buy banner/text link advertising from website owners.
I think you are talking about social bookmarking too. You may be talking about back links though. Usually all you have to do is register to the site, submit your domain, and then have other people "digg it" "stumble it" or what ever the site asks you to do to make it popular. You can get people on this site to do like 20 sites for less than $5. And then in the freebie section, you can get people to "digg it" sumble it" ect.