What is a FIDE ID number?
Any chess player who has a FIDE rating or provisional rating for over-the-board chess is allocated a FIDE ID number. This number can be found next to the player's name on his or her ratings card. To find this information, go to http://ratings.fide.com/ and do a name search.
Before registering a FIDE ID, check the following:
Make sure that your arena membership details, in particular date of birth and the spelling of your name, correspond with your FIDE ID details.