When you place your first order we bill your card as you go through the checkout. This amount then sits on your account as "credit" to be used against any future orders. The amount of credit you see reflects what you have paid.
We operate a credit system because lots of customers earn credit by referring their friends - we give £20 credit for each friend who signs up to our service. Some customers go the whole year eating for free!!
You are free to change what you'd like to order before midnight on Thursday, so you could choose different priced recipes, or more or less meals.