Setup your default configuration items.
Open-AudIT Default Configuration Values and Description
Make sure if you wish to use Discovery, you have default values for default_* items.
Audit a single Windows computer.
https://community.opmantek.com/display/OA/How+to+audit+a+single+Windows+computer
Discover a subnet.
https://community.opmantek.com/display/OA/How+To+-+Use+Open-AudIT+Discovery+on+a+Subnet
Discover your Active Directory domain.
How to use Open-AudIT Discovery on an Active Directory Domain