Microsoft To Do is a simple and intelligent to-do list that helps you manage all your tasks in one place. In each list you can add as many tasks as you like. Select categories, due dates, reminders, and attach files to tasks. Since all your tasks are stored on Exchange Online servers, they'll also appear automatically in Outlook tasks.
Keep everything on track by setting due dates and reminders for each task and starring your most important tasks. Use steps to break down your larger tasks into more manageable pieces and notes to record extra details.
The main purpose of a To Do list is to provide yourself with a list of your priorities in order to ensure that you don't forget anything and are able to effectively plan out your tasks so that they are all accomplished in the correct time frame.
Use My Day to help focus on daily tasks. You can add new tasks directly to My Day, or add tasks from other lists, by selecting a task to view its details and then selecting Add to My Day
Some additional information about Microsoft To Do can be found here