To connect for collaboration with another user you will need to know their Passpack nickname or the email address associated with their account, once you have that information you can send them a connection request to begin collaborating with them.
Click on the File menu and then on New Connection
In the dialog that appears you can search for them using their nickname or email address
Once you have found the account you wish to connect with click the Connect button next to their name in the search results.
Enter a message so that the user knows why you are sending a connection request.
Click the Send button. Your connection invitation will be sent to the user, they will receive a notice by email and within the application. Once they accept the invitation you will be able to start sharing passwords with them.
After you are finished sending connection invitations you can click the Finish Adding Connections button to close the Connect dialog.