http://www.8notes.com/f/30_106945.asp?y=1&sterm=vibrato

You're right, it is asked a bunch. Next time, to save yourself some time, you can do a search to find those other threads where the same question was asked and answered.

It takes some developing...
The major pitfall is for it to become involuntary and uncontrollable. Make sure the vibrato you are using is controlled, intentional, and in good musical taste.

Man, this is really not something to try and learn over the internet. Do you not have a teacher you can ask in person?