Usually IP camera is web server that could be connected to Internet and you could view camera from any place that is connected to Internet.
What do you need?
1. External IP address. Preferably static, because in other case you need to use DDNS.
2. Correctly set up router. It should map corresponding ports to Internet.

Here is example of setting port mapping for ASUS WL-500 gP:

Here internal port is mapped to external port 80. It means you can simply type your external static IP address from each PC in Internet and IP camera page will be opened.