The tags system is basically something for the search engines.
Whenever you create a new thread or visit on old thread, you will see a small box where you can enter "Tags", these are basically keywords that are used to identify the main content of the thread. For example, if a thread is discussing skimmers, then enter the word 'skimmer' into the tag box.
It may also be of benefit to members because if they click on one of the tag words like 'skimmer' then it will bring up all threads that have been tagged with the word skimmer.
Anyway, this is not really anything for you to worry about, you can ignore it completely if you want.
This is a worldwide networking system that you can use to communicate and share with other members using this system from other forums, or, you can just use it as an extension to your profile, you can upload pics, run your own blog etc.etc. play around with it. Have a look at DragonReef's Zoints profile, he has started playing around with his one.