Public folders are special type of folders which are shared for reading to all users of the particular domain or of the particular mailserver (it depends on server settings). Public folders help especially share information across the company. For example, company's events are set in the public calendar so that everybody can see when the events happen and view their details, while the person who is responsible for setting of such events can see who is available for the corresponding event. Another advantage of this feature might be for example sharing of public contacts across the company.
If you want content of public folders to be available even when you are not online, follow these instructions:
In the window's menu, select .
Select folders you want to access offline. Click on Subscribe.
Folders will be showed in Subscribed Public Folders.