There was a diagram kicking about on here to show you what needs doing.
Iirc you have to unscrew the centre console that runs between the seats over the handbrake and up to the front console and lift it up and away slightly so that you can get the bracket in underneath infront of the rear ash tray if that makes sense and bolt the bracket to the body of the car, like S3 baby said, there is a little pocket behind the handbrake that should have a rubber mat in, you have to cut around the edge of that so that you can drop the armrest into position and attach to the bracket underneath...