Ensure that the inputs, timeline, and tracks are properly set up.
if there is nothing to the left of the editor window, press Ctrl+E or 'View > Show Editor Mixer'
Select the track you're recording onto
set the metering point to "input" and verify that it's working correctly and connected to the right thing (say what this does, and why you want to do it now)
See "Adjusting Recording Volume" below, and do it now
Arm the track for recording: either press "Record" in the track's mixer in the left, or press the small red record button on the track itself
the buttons will remain lighted to show that the tracks are armed
arm Ardour for recording by select the big red record button on the transport
start the transport in in the normal way (big play button)
when you're done recording, stop the transport with the big stop button
each time you start and stop the transport, a new "region" is produced
each time you stop the transport, Ardour "un-arms" itself, but any tracks that you selected are still armed
When you've finished recording a region, use the "Regions" box-thing on the right of the interface to rename the region:
Find the region that you just recorded (by default they are named like "Audio 1-1" which is the name of the recording track followed by a hyphen, then a number in ascending sequeuence representing the "take"). Select it.
Click on the title, and a box should surround it.
Change the name to what you want.
Press enter to finish editing the name.