Social bookmark links can be found by clicking the "Share" button.
Such sites allow you to store, tag and share links across the internet. You can share the links with friends and people with similar interests. You can also access your links from any computer you happen to be using!
If you want to save a bookmark for future reference or share it with other people, simply click on "Share" then on one of the links to add to your list.
All of these sites are free to use but most require you to register. Once you have registered you can begin bookmarking.
Each of the sites works slightly differently. Try the links on the right to find out which is best for you.
More information about social bookmarking is on Wikipedia.
For more details about a few popular services:
To signup (secure): Google+ - one account for all your Google 'stuff'