This is a very common question and although it is a simple concept to understand it is really hard to explain unless you are technically inclined.
The short answer is this:
Live Cams connects to your camera by an IP address and a port or a host name and a port. If you enter an IP address it is most likely only valid when you are connected to your home network. This IP address is not valid on the internet and therefore your iPhone/iPod cannot find your home network or camera. You need a dynamic DNS name (host name) that will always point to your router so that Live Cams can find the network where your camera is installed. After this you will also have to open the port so that the request for video will pass through your router and be sent to your camera.
That's short? I guess not, it's still rather complicated. Here's an article with greater detail that may answer your questions:
I recommend signing up for a free dynamic DNS account at http://www.dyndns.com