You can manage an ASA 5512 via any interface (assuming the rules are setup to allow it). It also has a serial console port for direct hardware access.
The best practice is to use the Management 0/0 Ethernet interface designed for that purpose but it's not required. By default the M0/0 port is used.
The appliance should have come with a quick start guide but here a link to it:
http://www.cisco.com/en/US/docs/security/asa/quick_start/5500X/5500x_quick_start.html
