In order to access the Apple online store, you'll need to register and log in with an Apple ID to the institutional store as an authorized proposer or purchaser.
Note: If this is your first time using the online store, you will need to pre-register on the Apple registration site. You can click here for Apple Online Store registration instructions.
Once you've created your Apple ID, you will be able to log in to the Apple Online Store.
If you have any questions regarding the registration process or need assistance, contact Apple's support team at user.support @ apple.com or 1-800-800-2775, option 6.