The two trigrams go next to each other. First one at left, second one at right. The time moves from left to right. First trigram is 'now', the second one shows the outcome, the future. The trigram oracle is much more fortune-telling than the hexagrams. There is also a lot of advice, but you have to look for it, more than in a hexagram where the line text usually is an advice (in the form of "if this - then that").
  If you want to turn the two trigrams into a hexagram, the second trigram goes BELOW the first one when you ask about your own concerns rather than about the outside world. It is the way one would write it on a narrow bamboo slip, from top to bottom.
   It is the more 'common' way, and it is more my style. I ask about what I can change or improve in my life, and seldom about things outside my own mind and life. I guess a king like Wen would prefer the other sequence - and he did so in the hexagrams.
  The changed lines with the red dot or cross (future: not changing but changed!) are in the second or bottom trigram. The situation now (my attitude now and my surroundings and my situation in them) is in the first or upper trigram.

  For anyone familar with the Yijing, it is clear that the two trigrams form a hexagram, but I don't think they started like that. In all cultures there are 'elements': earth, fire, water etc. Using two of them must have been obvious. King Wen combined them into a coherent whole and the duke of Zhou added explanations to the lines.

  I chose to leave out what refers to hexagrams. It will make querents jump to hexagrams right away, but this oracle is different. Less sophisticated but more direct. Another reason is that by contemplating this way of changing, one learns a lot about the trigrams (and hexagrams!) which is not clear when moving the other way, from hexagram to trigram.

  This oracle most of all tells you where this will go, the outcome. The future is based on your attitude and situation now, including your present needs and hopes, which you can see in the first trigram. But where will it direct you (second trigram)?

  If you want to ask about someone else or politics or whatever outside your own direct realm, then you can put the second trigram above the first. You still read the lines in the second trigram, but now it is the upper trigram of the hexagram.

  This oracle looks like a precursor of the YiJing. I imagine King Wen sitting in prison and occupying his mind with this trigram oracle. Saving his sanity. Moving the trigrams around. Thinking about what they imply, how they are more than 8 images of the visible world, but combine into a complex structure of the entire cosmos. Giving birth to the Zhou Yi.

  It is easy to turn the two trigrams into a hexagram and look it up in the Yi. The two are closely connected.

  The Chinese texts in this trigram oracle are a mix. Most come from the Neigua ChuwaiLi, which is its real source. If you are interested in the background of this oracle, then don't look here: there is a good translation in Harmen's astrology book and probably there are other translations as well.   I couldn't find it in ctext.org, but I am more interested in its working, so that is where I looked most of all. See the video of the Hongkong diviner Tin Yat Dragon