In Outlook 2011 for Mac, in the ribbon, select Tools tab, then click on Public folders button.
In Folder browser window, navigate through the public folders tree until you locate the folder you need to access. Highlight the public folder, then click on Subscribe button.
Once you have selected all the folders you need, close the window.
Note: You will need to individually subscribe to each public folder you need to access.
Open Mail in your Outlook 2011 for Mac. Under the Subscribed Public Folders you will see the list of public folder you subscribed to.