You need to download and install iTerminal Server.
Your firewall (if installed) must allow network activity for iTerminal server software on port 4506. Else you will not be able to use your host command line with iTerminal app. If you have troubles with firewall configuration please visit our forum and create topic with description of your OS version and Firewall software installed.
Run iTerminal App on your iPhone/iPod/iPad. You will see server in list of your hosts. Now you can send any commands from your iOS device to your host and it will correctly process them and send result of it processing back in realtime. It's so easy. Tap on host. Type your command. Get response.
If you want to use iTerminal via 3g you have to forward connection port (by default 4506) from your router to your host. Also you need that your router have a static IP address to connect with from internet or a dns name given by some service like dyndns. Then you have type that DNS name or static IP address in host setting on your iOS device in iTerminal app. Since that you will be able yo use your host command line from everythere there internet is via WiFi or 3G.
You also can install server software on PC using *.msi installer and Active Directories GPO.