Graphical user interface is nice, but sometimes is easy to be lost, even with simple tasks. Here is an example, how to setup static IP address 192.168.1.2:
Menu:
System/Preferences/Network Connections/
Panel:
Wired/Auto eth0/Edit/ Connect automatically IPv4 Settings Method: Manual Address: 192.168.1.2,255.255.255.0,192.168.1.1 DNS: 192.168.1.3,208.67.222.222