On the main dashboard page there is an option called "Dinner" - start by clicking here.
This will show you your current balance, as well as any recent deposits. The "Add Dinner Money" button will allow you to add more money.
Type the amount of money into the box, and then Add to Basket.
You can then go to your basket, from which you can check out - this is where it will ask for card details.
On the front page of the site there is now a "Dinner Money" box, which displays the current balance:
Type the amount you want to add, and click "Add to Basket". You will see that at the top of your screen the shopping basket is no longer empty:
Click on it to go to see what is in your shopping basket, and then click "Checkout"
On the checkout page click Checkout again, which will take you to the payment page. You can choose to add a new card, or to save a card to use later for convenience.