A link to your downloadable products is provided in your order confirmation email. If that email has not yet arrived or you can no longer access it, downloadable products are always available after purchase in the "My Downloadable Products" section of your account.
(If you are not currently signed in, click the "Sign In"icon at the top of any page.)
Once you are signed in, you'll be directed to your account dashboard. You'll find a link to "My Downloadable Products" in the left-hand account menu.
If you purchased an MP3 and the audio file begins playing instead of downloading when you click its link, you'll need to first save the file to your computer. Just right-click or control-click the name of the file and select "Save Link As..." or "Download Linked File As..." This will allow you to select a destination and begin downloading the file to your computer.