Adding photos to Flickr, uploading a video to YouTube or writing a post on Wordpress. All these Social Media websites support Tagging. A lot of people either dont know how to use Tags or dont even know they exist.
Tagging your content online is very important and just by entering a couple of keywords it can increase your traffic and bring you more exposure. When websites ask for Tags they want you to enter keywords relating to that piece of content.
These Tags are used by search engines, social media websites and other services to link people to the content they want to see.
Heres an example:
I upload a video onto YouTube about social media and the internet. I would add the Tags: Social Media, Internet, Facebook, Twitter, Social Networking etc…when a user searches these keywords my video will appear. If I wrote a post on Wordpress and included the above Tags, users can click on them and find other posts relating to that topic.
When you join a website, be sure to Tag things. Meaningful keywords that relate to the content your producing. I would recommend adding between 10 - 15 tags and make sure you keep them related.
Good luck and get tagging!