If your server has more then one IP address, you can enter there the additional IP addresses, one IP address per line.
my server is behind a router in a DMZ, now that means it has a private ip. can i put my public ip in this box and use it or will it stuff up because my public ip isnt local to my ISPconfig server? as adding dns records is a pain because i have to go round manually and edit them all or is that just something i have to do?
You have to put your private IP addresses into that field (the ones you see when you run Code: ifconfig on the shell), not your public IP address. You can use the DNS-Manager to create DNS records.