I'm a nanny and want to know how childcare vouchers work?

Hi all, basically i'm a nanny and earn �8.00 GBP per hour, the lady who i work for keeps bugging me to get 'ofsted registered' so she can use some childcare vouchers, which i understand makes it slightly cheaper for her?? However, how will this affect the �8.00 i earn per hour? don't quite understand ???.... and how will i get paid??