I have seen the four buttons at the left corner of each post and also on other websites. Can someone please explain how the tagging works? I believe that they will be helpful in the promotion and marketing of my websites.

I'm assuming you mean the Digg/Furl/Technorati/del.icio.us buttons.

Simply put, the idea behind the buttons is that they're meant for users to be able to "socially bookmark" sites that they think are useful under certain keywords, or "tags". By "socially bookmarking" pages, users can share them with other users and give them useful content to look at...in theory.

Now...the problem with these sites, in the practical sense, is that idiots often try to game them by spamming their own content in there constantly, often forming cliques and turning the social bookmarking concept into nothing more than a popularity contest or search engine manipulation.

So...my suggestion to you would be to add the buttons, but let users define what they mean. If users actually add your stuff, it's useful. If not, then you'll need to work on it.

Social bookmarking is often misused. Its the truth. But, I think all those dweebs who actually do spamming wont get that much popularity. Expecially from digg and others where other users also should flag it as useful. And, del.icio.us can be used by the spammer to put links on his own page. He cant actually get others to work for his anti-"social bookmarking" purposes. Thats why social bookmarking is still going on, providing useful content to a lot of users without damping their feet in spam.

How do I allow my visitors to define the content themselves? The links on Webmaster-Talk seem to have their values defined already.

Pass it in the URL as a querystring.

In the case of digg, title=(your keywords) and in the case of furl, t=(your keywords).

I added the social-bookmarking links to one of my sites a few days ago, and since the content on my site is unique and worth reading, so people are bookmarking it quite rapidly.

Has worked quite well for me uptil now.