...send some sensor data continuously to 'PC' far away with my friend via internet, with the help of my Ethernet, my PC and Arduino...
The good news: I tcan be done! And you've identified the way to do it.
The bad news?....
I don't know about "Network programming"...
You'll need to learn.
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Half the problem is that you'll have to learn a whole bunch of things all at once... building and running a server (that topic alone has multiple sub-topics), HTML coding (you won't need more than a smattering)
The other half of the problem is at the receiving end. More details needed of the receiver's exact needs.
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More good news... it CAN be done!! See http://ArduServer.com for some encouragement, some further information.
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Does your friend need continuous access to what, say, the temperature is where you are just when he's curious? I.e. is it enough to set up a webpage which can be accessed anytime, and the webpage shows the temperature now? That's fairly easy.
Does your friend need a graph of what the temperatures (or whatever) have been for the past few days? Might be a job to do with a PC at your end, rather than just an Arduino. See Overview of FarWatch products- surveillance via internet
Another answer, which would need just Arduino and a lot of work (and an always-on internet connection) is Pachube... If your friend needs a graph of up to 30 days' data (longer if you pay... 30 day service is free). More on that at Pachube for Sensing and Control- SC1wy