First: Click and hold the food icon for the item you would like to donate; the item will be highlighted on the shopping list. Drag the icon to the shopping cart; your donation will be indicated on the shopping list.
In the quantity column of the shopping list, use the plus (+) sign for each item to enter the quantity you would like to donate.
Second: When you have completed your shopping, click on the word "Checkout". This will take you to the secure transaction page, which allows you to "pay" for your donation by credit card.