On the Options window that opens, select the right-most tab, “Delegates”. In the Delegates tab, click on Add.

Type in the username of the person you want to give access to. It should appear in the list below. Select the user, and click “Add” and then “OK”.

Select which permissions you want this person to have. Be careful here, as the more permissions you grant, the more access this person has to change anything in your account. If you just want them to be able to see your folders, set their access to “Reviewer”. If you want them to be able to create their own items, but not change existing things, set their access to “Author”. If you’d like them to have full access to add, change, and delete items, set their access to “Editor”. Finally, if you would not like them to have any access to certain areas of Outlook, set the option to “None”. Once you’ve selected the different access levels, click OK, and then OK again.