How do I configure the /etc/network/interfaces file?

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http://askubuntu.com – I tried to access a wireless device on my kubuntu system and I have no access network to the network. I gave up on wireless and went back to my wired connection. How do I add a device to /etc/network/interfaces so that /etc/init.d/networking start will restart my network interfaces? Many thanks, Steve (HowTos)