Below are the intros to some of the top social networks:
MySpace - MySpace, available at http://www.myspace.com is the first website that comes to mind when the term "social networking" is brought up. MySpace is one of the original social networking websites, and it has an enormous base of users, making it one of the top social networking sites. MySpace connects users who share interest in music, books, television shows, videos, pictures and profiles. Users can maintain a list of friends, a gallery of images, a personal profile, and comments and other forms of communication in order to network, and keep in touch with people all over the world.
Twitter - Another popular social networking medium that is conjured when social networking is mentioned, Twitter (http://www.twitter.com) brings about a completely unique form of networking called micro-blogging. Micro-blogging involves creating updates in micro-format. Subscribers to your Twitter feed can keep up with your micro blogging updates throughout the day much in the same way that they would with an RSS feed or a standard blog, only the micro format makes writing in a Twitter account much easier than other forms of blogging and social networking. Twitter even allows for mobile updating, so you can update your followers on your status from anywhere, no matter where you are.
Facebook - Facebook (http://www.facebook.com), like MySpace, is a large scale social networking site that is known for providing many different avenues for communication and community facilitation. Facebook offers a lot of unique applications and games that make networking even more enjoyable among friends, business associates, colleagues and family members, making Facebook one of the top social networking sites online to date.
Livejournal - Livejournal, found at http://www.livejournal.com, is a blogging platform social networking site, which means that the community and communication facilitated is all based around blogging. Each user has a blog account, and users can join communities and leave comments in other blogs or journals in order to network with users from all over the world.
Flickr - Flickr, which you will find at http://www.flickr.com, is a unique form of social networking because it revolves around photo sharing. Users create accounts and fill them with their favorite photos, and other users can leave comments. Flickr photos can be commented on, tagged, edited and shared, facilitating communication and networking purely through photography.
Digg - Digg, found at http://www.digg.com, is another unique form of social networking that revolves around sharing media and news with other users in the community. Digg focuses on allowing users to unveil news and other media, allowing other members to comment and rate the media based on popularity. The more users "Digg" a certain piece of media or news, the more popular it will become within the community!