Next week a guide about net balancer will be available.
At the moment I can tell you:
1) add ETH00 and ETH01 in the NAT list in the section [Router][NAT]
2) add the gateways 188.8.131.52 and 184.108.40.206 by clicking on the button [Add] of the section [Net Balancer][Manage]: in the form that appears you just have to fill the IP of the gateway and the description
3) enable the Net Balancer
4) if you want the failover mechanism works correctly enable the [Failover Monitor] and add at least one external IP to ping. You could use the IPs of the gateway as Failover IP Addresses but external IPs are better.