Ok I can help! Me me me!
You have to book a CBT test, try looking on
http://dsa.gov.uk/AtoZATBINFO.asp?cat=295 for your nearest CBT centre. For that all you need is a spare day, a helmet and riding protection clothing (leather/bike jacket, gloves, jeans if you don't have riding trousers). If you are buying a helmet you can get one for about £40 for the cheapest one, but don't ever buy one second hand as - same as child car seats - you can't be sure if it has been in an accident before or not.
It costs about £60 (or around about that) and when you pass your CBT certificate allows you to ride on L plates for upto 2 years. If you don't do your full test before the end of 2 years, you must retake your CBT, which isn't much hardship really.
The day goes that you spend a morning learning basic theory, which lanes to take on a roundabout, etc etc basic driving safety theory. Then the afternoon they take you to a practice site (mine was a school playground on a weekend) and they show you the controls of the bike/scooter, how to hold it, start it, ride it etc. Then they test that you are happy with turning, indicating, pulling away from a junction, braking etc etc. When they are happy that you can safely ride it, they will take you out on the road for an hour or so with helmet microphones and take you for a practice ride, making sure you use all the things that you practiced and that you are safe on the road.
After that day you get your certificate! Easy as.
On the day you can choose to learn on a scooter or a 125cc motorbike. I personally have done 2 CBT's.. one on each.
Hope that helps?
If you need any more info on bikes/equipment/scooters/CBT's etc just let me know