You can find the installation files via the following link: http://onlinehelp.microsoft.com/en-us/office365-enterprises/hh180727.aspx the site also describes how to install the software. ( select option 3 Lync for Mac 2011 ) to download the DMG file.
When you try to log on you need to use your email address ( 2 times ) 1 time for email address and 1 time for user ID.
The message “Sign in to Microsoft Lync failed because the service is not available or you may not be connected to the internet” is not really normally but it’s a bug or a feature. Who will know. You can avoid this message to change the settings via Advanced.
Click on OK when finished. Try to login again.
If you have outlook 2011 for mac configured you can directly create a mail or calendar appointment via Lync.