Netmeeting is about as simple as it can be. You click on New Call and put in the address of the person hosting the meeting. The connection happens over TCP/IP.
The reason you do not make a straight connection to the target IP address has to do with the way the program allows multi-person meetings. It should not be an issue, since it happens unseen in the background.
When you run IPCONFIG you see an address for your ethernet card. This is your machine's address.
The gateway address isthe address of the router (could be your DSL modem, or could be the router at the far end of your DSL connection), which gives your machine access to the rest of the internet. It is the responsibility of that gateway router to send your traffic to the proper point on the internet and to send internet traffic addressed to you back to you. The gateway address is typically supplied to your machine automatically by the DHCP mechanism which provides your machine with its IP address.