The main idea behind this Soundscape tutorial is that you can generate ambient sounds in many different ways. If you play a guitar most likely you will play it with your fingers or a pick, in some cases you would use a bottle neck, an E-Bow or even an ordinary bow. But don't forget that your main task is to make it resonate - no matter how... Here I play strings at the end of a neck and bump my guitar with fingers.
I used this "bumping" technique later in an YBM ambient session - you can check it here: YBM "Ambient Session #2"
If you use a volume pedal and a couple of delays you can create pretty smooth musical noise. To make it musical - hold a chord and let your guitar resonate while you bump it, rub, shake or whatever... I would recommend turning down dry signal on your Delay and raising wet signal up. Tweak these parameters to avoid harsh sound with fast attack - what you need is slow attack. Actually slow attack is the key to any ambient sound. That's why ambient guitar players use volume pedals a lot.
Normally you would like to thicken layers with additional swelling chords. You can use vibrato bar at the end of the swell to swing the chord a bit. I always add a bass layer that would usually follow the harmony.
At the end of the soundscape I play a melody or some kind of solo... This time I decided to add an odd rhythmical structure. How to make this sound: I used 2 Deleays, 1st on Roland VG-99 → 390 ms, 2nd on Strymon Timeline Delay → 780 ms in dotted quarters. Play fast 2 or 3 notes of a chord - there's no need to play it in bpm time, though you can do it, of course.
You can listen to / buy this track on my Bandcamp page.