The general operations regarding Shared widget libraries can be found in the main menu 'Widgets->Add/Remove libraries' under My Libraries tab when connected to your account.
All the share options are grouped in a single drop-down menu item. This menu will always display the same options but they will be enabled or disabled depending on the privileges you have over the current library. To access the dropdown you have to click on the 'gear' next to the library's name and mouse over 'Share Options'.
The library controls will also be enabled or disabled depending on the privileges the current user logged has over the library being shown. All these operations will only perform changes locally and they will not be shared until you decide to commit them.
Once connected to your account and retrieved your shared libraries from the server, they are kept locally so you can work with them offline. In order to use them offline, just open Justinmind Prototyper, and if you synchronized previously the libraries with your account you will see them in the 'Widgets' panel or by clicking on 
and going to 'My Libraries' tab.
Notice, however, that you will not be able to commit any changes made to the libraries until you have access again to the Justinmind servers.