Hello, if you look at the Edenred website which is www.childcarevouchers.co.uk
(I think that's right) there is a brilliant FAQ page which tells you what you need to do as an employer or employee. We recently set my nanny up on there so I could use my vouchers with her and it took 5 mins and she was set up within a day.
In terms of registering your company, as the previous poster says - whoever deals with payrole needs to set it up as whilst they take the money from your gross salary and pay it Edenred, they also need to make the correct adjustments on your payslip.
Oh, and the amount you can put in depends on whether you are a basis rate or higher rate tax payer (government changed it a few years ago, so higher rate weren't getting a bigger saving).
I'd look at Edenred website as it explains everything!