Now that you have Exchange Credits in your account (by either earning or purchasing them), you can use these credits to purchase a study resource that suits your needs. Below is a brief summary of how to purchase a document using your Exchange Credits.
1) Find the document you are after.
2) Select 'Add to Cart' on that document.
3) Go to your 'Cart' and select 'Proceed to checkout'
4) Complete checkout. This will use your existing Exchange Credits if you have a sufficient balance. If you do not have enough credits, you will be provided with relevant options at the checkout page.