They're easy enough, by which I mean that their operation is apparent by looking at them, though there are a couple of mistakes worth avoiding!
If using the upper level, then the bike-carrier pulls forward and then the front (with the red handle) drops down. Its balanced so doesn't suddenly fall. Simply push the bike forward and attach your lock. You'll see there's a 'U' hoop which is hinged and holds the wheel, if you forgget to use this then your bike will only be held in place by your lock.
To finish, lift the bike-carrier up again to the horizontal by the red handle and push it back so that iits berthed in line with the others.
Using the lower level is easier because its just roll-on - roll-off without having to move the bike-carrier, but while bending down to attach/release the lock, you do run the risk of banging your head agaist the hard steel of the rack above!
There's usually plenty other people around to help you if you get stuck.
Its worth getting used to these racks as they appear to be coming more common across the UK and I guess their introduction is likely to continue.