Starting today the To Do service on Office 365 is leaving the preview mode to be generally available.
To Do is a service to help you tracking your tasks.
As Office 365 administrator, you need to manage your To Do settings (enable / disable) from your Office 365 administration portal below the Settings\Services & add-ins section
Then you have to enable (or disable) the license for To Do – which means you may have to update any script you are using to automate licensing assignment – the Service Plan for To Do in PowerShell is BPOS_S_TODO_2 or BPOS_S_TODO_3 depending of your Office 365 subscription
Then your end-users will be able to start using To Do from the web (https://to-do.microsoft.com/) or using mobile apps