Escalation policies make sure an incident never goes unhandled. If the first responder doesn't acknowledge an incident in time, the policy escalates it to the next person or team.

Go to On-call, find the escalation policies section, and click Add policy. Then give your policy a name and build its escalation rules.
Each rule says who to notify and when:
Rules after the first one fire only if the incident still isn't acknowledged, so each step escalates further.
You can repeat the whole escalation if nobody acknowledges the incident:
An escalation policy won't be triggered until it's linked to a routing rule. Create a routing rule that targets your policy so triggered incidents actually reach it.