You can find more information about your iMac in System Report, in Apple Diagnostics, and through online resources.
System Report. To get information about your iMac, use System Report. It shows you your hardware model, the serial number and operating system version, how much memory is installed, and more. To open System Report, choose Apple menu iMac Support.
AppleCare support. If you need assistance, AppleCare representatives can help you with installing and opening apps, and with troubleshooting. Call the support center number nearest you (the first 90 days are complimentary). Have the purchase date and your iMac serial number ready when you call.
A complete list of support telephone numbers is available on the web at Contact Apple for support and service. Telephone numbers are subject to change, and local and national telephone rates may apply.
Your 90 days of complimentary telephone support begins on the date of purchase.