Setting Up WIFI

[pauljoanss]

I am new to Linux so continually working in a bit of a fog.
Have written Xbian image to SD card and successfully started up PI and XBMC started automatically. Worked ok with internet cable but want wifi so have bought a small USB wifi thingy.
To try and connect to wifi I started up then exited XBMC and arrived at a dialogue box which allowed me to set up wifi info. After exiting the dialogue box there was something going on but got the impression all was well.
I was then left with the Xbian command line and at this point I have no idea how to restart XBMC.
Tried powering off and then restarting straight to XBMC but found no wifi connection. Not sure if it was connected first time or it does not store connection data when power lost.
I think this is a very simple problem but my lack of knowledge makes it impossible.
Any help would be welcome.