Each To Do will be stored in the To Do sections, on your profile and on the main column. As Admin you can view all to Dos for all users.
For manger you will be limited to your To Dos and your Teams and as a user you will have you own only.
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The main To Do tab:

Via the main To Do tab you will see all as Admin if need be, use the 'All to dos' to see everything.
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As a user and manager you will be limited to your own To Dos.
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The filters are key here to find any specific to dos or to show historic To Dos - please see the screenshot below for guidance on filtering.
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