Restoring a Outlook backup:
1) Go to File and select Data File Management
2) Click on Add and choose the type of Outlook Data File which you want to import. Unless you are using Office 97-2002, most probably, it will be Office Outlook Personal Folders File (.pst).
3) Select that and choose OK.
4) Outlook will be restored to the same state which it was when you backed up the pst file.