Use the Add-MailboxFolderPermission cmdlet to add folder-level permissions for users in mailboxes.
To modify the permissions that are assigned to the user on a mailbox
folder, use the Set-MailboxFolderPermission cmdlet. To remove all
permissions that are assigned to a user on a mailbox folder, use the
Add-MailboxFolderPermission -Identity firstname.lastname@example.org:\Calendar -User email@example.com -AccessRights LimitedDetails
this example share Ayla as a calendar to Julia's mailbox, And view availability data with subject and location.