There was no manual in the box. Try google and apple.com as well as the OS itself for the usuals.
I think the word "roaming" is odd here. I would have looked in the Apple Menu > System Preferences > Network button then:
TCP/IP tab and/or connfigure via AirPort or other wireless (WiFi) Ethernet).
We have a MacBook Pro acquired 2nd hand so no manual. Want to go on roaming when out of range of wireless provider but can't work out how to do, can see that in the network settings that "roaming" is off but can't see how to turn "roaming" on. Any help?