For starters, be sure to configure a vCO Endpoint (Infrastructure tab -> Endpoints -> Endpoints). In a POC or small environment you can point to the embedded vCO instances that ships with the vCAC VA. Otherwise point to an external vCO instance (note: if using an external instance, be sure to install the NSX 6.1 vCO plugin first).
Once the vCO Endpoint is configured, it’s time to add NSX support to the vSphere (vCenter) Endpoint. In vSphere (vCenter) Endpoint configuration, check the “Specify manager for network and security platform” box and enter the appropriate address / credentials for NSX. Be sure the account used has admin permissions (you can use the default admin account, or any account that has been added as NSX Admin users.