If you are running an older Mac and you need to purchase Mac OS X 10.8 Mountain Lion, for example, you can opt to purchase it from the online Apple Store. You will receive an email with a content code for the Mac App Store, usually within one business day.
To install the software, users will need to visit the Mac App Store, where they can redeem the code they received via email and then download it.
Prior to this, customers could purchase a copy of Lion only via a phone call to Apple. Customers who have previously purchased either Lion or Mountain Lion can download the software from the Mac App Store through the “Purchases” tab.