AD Connector: how to synchronize passwords

I am reading the AD connector manual and, in section 9.3 I see I can choose “configure ucs as part of an active directory domain” or “synchronisation of account data…”
I started with a fresh UCS installation and it never presented me that choice, and now I have again a system configured as first option.
How can I reconfigure AD connector to try password synchronization?
Is there a deep explanation of differences between two modes?