You need a 24x7 connection from the TrueNAS in question to the TrueCommand server - preferrably at the same location or through a VPN - to use TrueCommand. It’s an enterprise/data centre system management appliance for a fleet of TrueNAS systems as @dan already wrote.
It does not help with the “remote connection” part, that is assumed to exist.
I run one for fun/curiosity - see the screenshot for the status dashboard of my TrueNAS “fleet” of three systems. Yes, I have three TN servers that are always on, just like the virtual machine running TrueCommand.
