So when you open Ardour and create a new project or select an existing project it will bring up the “Audio/MIDI Setup” menu. It sounds like you already have your UX1 selected as your input and output device. If not, start over and be sure to do this.
Once your session is open, you need to first create a track for the guitar. With Shift+Ctrl+N you will bring up the new track dialog. You want this to be an Audio track, and probably mono.
Now that you have a track there for your guitar you have to take care of all the routing. You can bring up the “Audio Connections” menu with Alt+N or from the Windows menu on the toolbar. The vertical axis of this menu is your inputs and the horizontal axis is the outputs. First you want the guitar to feed to the new track you created. So on the vertical axis select the “Hardware Inputs” tab and on the horizontal axis, select the “Tracks” tab. Create a connection from the UX1’s input to the new track you created for it.
Next, that track’s audio has to actually go somewhere. So on the vertical axis, select the “Tracks” tab and on the horizontal axis select the “Busses” tab. Create a connection from the guitar track to the master buss. Since your guitar track is in mono you probably want two connections here, one to the left channel of the master buss and one to the right channel (or else you will only hear the guitar in one side of your headphones/speakers).
Finally, the master buss needs to feed back to the monitoring/output channels of your interface. On the vertical axis, select the “Busses” tab, and on the horizontal axis select the “Hardware Outputs” tab. Create two connections from the Master Buss to the Outputs of your UX1. Left channel to output #1 and right channel to output #2.
Hope this helps, its always a little crazy to explain this in words.