To let Revenue know that you have a new employee, you will need to submit a new RPN request. You can do this from the Employee screen.

Select the employee and click on the Tax tab. You will see a button with 'New RPN' on it. Click this button to send a new RPN request to Revenue. If the request is successful, then the next time you retrieve RPNs in the Revenue>RPN screen the new employee will be listed with their tax details.

NOTE: If the employee has been previously employed by you, please follow our Re-employing people guidance instead.

For PAYE Modernisation, the P45 process has changed. You only need to include a leave date for the employee.
Pay the employee in the Payroll screen (Before entering a leave date), if you need to.
Click the Leaver (P45) button in the employee screen as usual and enter a leave date and update the employee.

The next payroll submission will inform Revenue that the employee has left. Note that the employee will still appear in the submission screen, even if they were not paid for the period.
You no longer have to issue a P45 to the employee.