Go to top right corner of page besides your profile icon you can see To Do List icon, click on View All button now at calendar page right side you can see all your task click on + icon button, at this modal window enter Title and Date then click on Save button.

To complete To Do task click on check box so it will mark task as complete. For edit To Do task click on edit button icon and for delete To Do task click on delete button icon present at To Do List.