A security domain is a unique set of security controls that are assigned to a cell, node, cluster, or application server, so that different cell, node, cluster, or application server can have their own, unqiue security settings. If Global Security is enabed, a security domain will override or take precedence over global security. If Global Security is not enabled, a security domain can be used to apply certain security controls to a cell, node, cluster, or application server. Security domains can be used even if Global Security is not enabled.
You must have the Administrator, Configurator, or Admin Security Manager role to be able to create/change/update/delete a Security Domain.
At a high level, these are the common steps to set up a new security domain.