Make sure you already have an account, are logged in to your account, and have at least one product in your shopping cart. Once you are ready to check out (actually buying the products in your virtual shopping cart), just click the "Check Out" button on the top right side of the page - directly above the "Your Order" box. This will take you to the payment page which should already have your mailing information that you gave us earlier. If the address shown is not correct then click the "Change Address" button to make any needed corrections.
You will then need to check which payment type you would like to use. If using a credit or debit card then check the box (by left clicking on it) next to "credit card" which is located directly under the "please select" arrow. If you would rather use PayPal or use a store credit, then you would check the appropriate box for those. Assuming you are using a credit card, you would then fill in the spaces provided with your credit card information and click "continue" at the bottom of the page. This will take you to the "Order Confirmation" page which will give you the details of your purchase.
If everything on the Order Confirmation page looks correct, just click the "Confirm Order" button at the bottom of the page, and you will be taken to a page that says "Your Order Has Been Processed" at the top. This page will have a listing of the products you have just purchased. You actually download your products from this page.
To begin downloading your purchases, just click on the title you want to download and the process of downloading the book will begin. You will be asked if you want to open the file or save the file, please choose to save to your desktop.
Note that some web browser will be set to block pop-up windows or any downloads and you will have to manually override that setting to complete the download. For example, in Internet Explorer you may see a warning bar display as in this image below:

Just click on the warning bar and choose the option to allow the download of the file, then choose to save the file to disc.
Once saved to your computer's desktop, you can then open the document by simply double clicking on the icon on your desktop and it will open in Adobe reader.