USB devices such as memory sticks should automount on kealia, and be accessible for backing up your data. Insert the memory stick into one of the USB ports in the front of the CPU.
Use the df command to make sure that a device called /rmdisk is now available. Once it is available, you should be able to use standard UNIX tools like cp to copy your data onto the USB device.
To safely remove the USB device, type eject rmdisk.