LiveJournal implements syndication by creating "Syndicated Accounts". Syndicated Accounts are similar to regular journals, except that the only way they can make entries is by receiving an updated RSS file from a host site. For more information on Syndicated Accounts, please read lj://faq/150 . If you are having trouble with a Syndicated Account, please read lj://faq/151 .
If you would like to try to find some Syndicated Accounts to add to your friends list to experience the Syndication system, please read lj://faq/163 .
To help the system's performance, users can only add a certain number of Syndicated Accounts to their friends list. For more information on this restriction, please read lj://faq/153 .
Syndication files are in RSS format. Any site that has an RSS syndication file can be added to your friends list as a syndicated account. RSS can be explained like this: First, the site you're syndicating gets updated. Then, the site updates its syndication file with the new content. Finally, LiveJournal checks the site's syndication file, notices the new content, and creates entries and posts them to the Syndicated Account's journal.