hi - to see your ethernet card you type:
as root. This should show all ethernet interfaces on your system. normally you would only need to configuire it manually if you are setting a static ip address for your local ethernet lan connection. To set a static address type:
ifconfig eth0 10.9.8.1 netmask 255.255.255.0.
then type: ifconfig -a to check that the setting is correct. You would need to change he above to your particular system. If you have more than one ethernet card, the first would be eth0 then eth1,eth2 and so on. The ip address for a local lan can be anything you want, but the combination of ip address & netmask must be similar for machines on a lan to communicate.
But, your trying to get on the net. What you need to do will depend on your modem. I can say that if its a cable modem, you need to set the card to discover its ip address by a program called DHCP. Depending on your distribution, there should be a simple way of doing this in a gui. In my system i would select configuration from the start menu > networking > netconf, or simply go to my control panel.
Once you set DHCP, unplug your cable modem for a few minutes then reboot your system.
If you have a normal modem im not sure how you would go about things though. If you say what kind of modem you have & your linux distribution someone will be able to help you on the right path.
I use Mandrake 9.1 & its really simple to set up a internet connection for a beginner like me.