Energy Efficiency Rating's (EER) are supplied by your home builder, architect or an accredited assessor. EER refers to your home's passive energy performance and can be used by buyers/tenants to consider their likely energy costs and to compare them against other properties.
This field is only mandatory in the ACT so if your property is located in another state and you do not know the energy rating, you can safely ignore it.
If you do not know your home's EER and are required to or would like to enter an energy rating, you would need to have an accredited assessor supply you one. You can learn more about EER here.