After you've completed your purchase, your reservation will be marked as Payment Pending and then soon after Active (there's a third possible status, which is Retired).
Once your reservation is Active, the discount will automatically apply to matching instances. AWS refers to this hourly discount as a billing benefit.
Choosing a Convertible reservation class immediately rules out anything but a 3 year term. In return, you get a little more flexibility than the Standard reservations because if you decide the reservation no longer meets your needs, you can convert it to a reservation that is of equal or higher value, paying the difference of course.
If you made a reservation for a specific Availability Zone, AWS also provides ...
