It's a simple process:
1) Download a form from the internet
2) Fill in pages 1-3 of said form
3) Scan completed pages 1-3
4) Scan your certficate of insurance
5) Scan your Tax Disc
6) Scan your Vehicle Registration Certificate
7) Compile and email the above to NTA within 30 days of the motor tax issue date
Wait up to 20 days for the same to be processed
There's a postal option for those who are ill-equipped to complete the electronic process.