An action group is a collection of notification preferences that can be used by Azure Monitor to send alerts to users or groups when an alert rule is triggered. An action group can include email recipients, SMS recipients, voice call recipients, webhook URLs, Azure functions, Logic Apps, and more. To send an email message to two users named User1 and User2 when CPU usage on VM1 exceeds 80 percent, you need to create an action group that contains their email addresses and associate it with the alert rule. Reference:
Create and manage action groups in the Azure portal
Create, view, and manage Metric alerts using Azure Monitor