Office 365 (Web) - How to create and edit Tasks
How to create and edit a Task in Office 365 Web
To create a new task, click new task. This will open a simple task form in the reading pane.
If you want to have more details, click show more details.
When you’re done, click Save to save your changes or Discard to cancel.
To edit a task, select it in the list view, and then click Edit in the reading pane. When you’re done, click Save to save your changes or Discard to cancel.
Flagged messages will appear just as they would if you were viewing your Mail. You can respond to them from within Tasks. You can change their flag status by right-clicking the flag in the Task list and then clicking the value you want.
When you edit a task, you can click the More menu to see more things you can do. Click it to see options to delete, add a category, or mark the task as complete.