Well, I havent played in a few months, but as far as I remember from PRSP it goes something like this.
Youll firstly need Hamachi - you can get it
here, I cant find where I downloaded it but it should be free, if that link doesnt work then use google to find Hamachi free version
After you have it, create a new network, and get your friend to join it by him also getting hamachi, its quite straight forward getting a network together. After youve done that move on;
Go into Singleplayer - Host Game (or through Online or similar)
Set up your game, map, settings etc, and then start it. Tell your friend when you are loaded in.
Then, get him to use Singleplayer - Join IP (again, its somewhere there but I havent seen the screen in 2 months)
He then types in the IP address which he gets from your profile on hamachi.
Then by simply selecting Go, he should connect directly to your game.
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Could anyone clear up any innacuracies I have?
After you choose your settings