This tutorial will show you how to setup an alert in SharePoint Online.
SharePoint Online Alerts
In this example I am going to be setting up an alert to send a daily summary of all tasks completed, that will shoot off at 5pm.
Click into your SharePoint site. Click on “Tasks” on the left hand side.
Then click on “Tasks” in the ribbon.
Click on “Alert Me” and click on “Manage My Alerts.”
Click on “Add Alert.”
Select “Tasks” in the list and click “Next.”
In the Alert Title section I name my alert “Daily Task Summary.” Enter your email address (by default it will most likely be already filled in), and then copy the rest of the options in the screenshot below. You can see this will be set as a daily summary that is sent at 5PM.
You can tweak the options above to perform different options. The one thing we can’t seem to figure out is how to send an alert only on completed tasks. But hopefully the above helps.