10.04 has Network Manager installed by default. I'm assuming you have Gnome installed, ( you said Ubuntu not Kubuntu, or Xubuntu ) so look for the icon on the top bar. Click it to start configuring.
You can configure wireless or wired connections. Which is it you are configuring? Do you have a router, or are you connecting the system directly to the modem? Is it a modem/router? Make and model please, we can not see your hardware.