If the control panel is displayed with icons like THIS you can click Network and Sharing Center and skip to step 4.
If the Local Area Connection has a red X like THIS make sure there is an ethernet cable connected to your computer.
Make sure "Obtain an IP address automatically" and "Obtain DNS server address automatically" are selected as shown.
If it is then your computer is properly setup for an Ethernet connection. If you still can't get online double check your router or modem or contact Tech Support.
Hover over the image to zoom.
This tutorial shows you how to check your Local Area Connection properties to make sure they are set correctly for an internet connection.
Click on the steps to show the screen shots.