Registering:
There are three steps to before you can claim for Gift Aid:
Register with HMRC for Gift Aid. A presentation which shows you how to do this can be found here
Ask all Parents to sign the Gift Aid form. A sample form that you can download can be found here and a short presentation can be found here
Register for an online account with HMRC. Once again, there is a presentation which shows you how to do this and it can be found here