1) Go to your homepage and click in the top left corner on your name.
2) Look in the address bar at the top of your browser and then;
If you have a Facebook Username copy all the text after the final / (This is with Firefox, all browsers will look approximately the same)
If you haven't, like Marc, copy the NUMBER that is at the end after the =
3) That will be your UID. So, for example, using our Admin Marc, the UID is: 100002092703851