You can't do ... anything ... related to computer-to-computer gaming without a network. Servers are required for such gaming.
Server in computing: a computer or program that supplies data or resources to other machines on a network
(source: dictionary.com)
Basically impossible without a server.
UNLESS
Your friend's computer is physically close/next to your computer, and you both connect your computers directly by using only an ethernet cable. One end to your friend's computer, the other end to yours. Simple. But not simple because you then have to configure your computers' networks to read off of each other directly. I forgot how to do that, which is sad because my college classes taught me stuff like this.
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