Usually Fedora auto-configures to use DHCP for setting the IP address, and someone has set that service up on your LAN. Your machine should get an IP address automatically.
Open a terminal emulator (Applications->System Tools->Terminal) and check the output of the following command :
$ /sbin/ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:9A:BD:9E:12:9F
inet addr:10.0.0.1 Bcast:10.0.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
The output shows the device eth0 is "UP" and "RUNNING" on inet address 10.0.0.1
If you need to set the IP address manually your system administrator, or someone familiar with the LAN, tells you the value. You can set it via the menu option "System->Administration->Network", enter root password, then adjust the Static IP address for the device connected to the LAN. Finally, activate the interface and check the ifconfig command output (above) as a check.