All PD alerts can flow into Rootly for incident management if desired. By now, you should have your integration between Rootly and PagerDuty configured, as well as the services on which you wish to alert.
To create an alert from PagerDuty, do the following:
Log into the PagerDuty account where you first created the new integration.
Click the New Incident button, which should be available from most pages within PagerDuty.
In the Create New Incident dialog, select the Impact Service, which should be one of the services you integrated earlier with Rootly. Add a descriptive Title, and fill in any other fields as needed.
Click Create Incident.
You will then be taken to the page for that incident.
Now, login to Rootly if you aren't already, and navigate to Configuration, then Alerts.
There, you will see the list of current alerts, where you can create an incident for that alert if desired. To do so, click the Create Incident button on the right side, and follow the standard incident workflow outlined previously.
When you create an incident in Rootly from an alert in PagerDuty, management of that incident can then be done via Rootly. Resolving the incident in Rootly will also resolve it in PagerDuty.