I will earn about €6,500.00 in Savings Certificates Interest in 2018. I have two questions about this. Will I have to fill out a form 11 for 2018 and what tax will I be liable for on the €6,500.00.
As above do nothing. Interest on state savings is fully Tax Free. You do not need to do/declare anything. Go and spend some of that tax free interest
on something nice
This is correct. You can always check out the SI that governs your particular issue. For example SI 422 of 2014 that governs issue 21 says: "4.1 The Interest is not subject to Deposit Interest Retention Tax, and is exempt from Income Tax, Pay Related Social Insurance and the Universal Social Charge. Savings Certificates in Issue 21 are exempt from Capital Gains Tax in Ireland."