I recommend using individual names or groups. In the Roles box, select the role you want to assign to the selected person, or create a custom role by selecting individual options below the Roles box. You need to give at least read and view permissions to the individuals in order for them to see your Calendar. This is because the permissions will not cascade down to your existing folders. The permissions you set up on the Outlook Today folder will take affect on any NEW personal folder you create.
NEW folders take on the permissions of the Outlook Today folder.
That means that every time you create a personal folder, you will need to check the permissions to ensure that only people that you want to have access to it actually do. In the Name box, type the name of the person who granted you sharing or delegate access permission, or click Name to select from a list. In the Folder box, click the folder you want to open. Then click Shut Down The Computer. Important Do not turn off your computer until a message appears telling you that it is safe to do so.