To configure dynamic IP address edit /etc/network/interfaces file in this way
auto eth0
allow-hotplug eth0
iface eth0 inet dhcp
To configure static IP address edit /etc/network/interfaces file in this way
auto eth0
iface eth0 inet static
address 192.0.2.7 your address
netmask 255.255.255.0 typical value is 255.255.255.0
gateway 192.0.2.254 router address