On the download page you need to put a link to the zip file containing the ebook. I usually upload the zip file to my website first then edit the download page so that I have the zip file link exactly right.

You will need to put a PayPal 'Buy Now' button on your index page to sell it. Go into your PayPal account, click on Merchant Services and follow through using the 'Buy Now Buttons' link to create a button. In the Advanced section (step 3) there is a place where it says:

Take customer to a specific page (URL) after successful checkout:

In that box you need to put the web address of your download page. So it is best to upload your download page before you create the button so you can get that exactly right.

Always test your sales process. Use a friend or family member's PayPal account to buy your product and then refund them (unless you have two accounts yourself). Make sure they reach the download page after checkout.

I would put an email address on the sales page and download page too in case people have any problems. This means they will contact you rather than complaining to PayPal if they have a problem with the download.