Some pioneering humans get stranded on a planet which has exactly the same conditions as the earth in the Triassic period. They decide to stay and build a society/colony from scratch with the available resources of the planet. How will they go about doing it in terms
Also, how would the environment bring about changes in the humans?
1) If it moves and isn't toxic, it's lunch. Dino eggs are excellent food and start damaging the number of local nuisances. Young dinos are also vulnerable unless they can outrun and out-think humans (as in not fall for dead-fall and pit traps). There's also shellfish, besides fish, and maybe large insects.
It ain't pretty, but the best way to get digestible green stuff may be out of dino stomachs, where they have been so good as to pre-digest it for humans. It's how many carnivores get their vitamins. (Fermentation tanks -- brilliant suggestion.) They need to look at edible fungi, lichen, and sea plants.
Considering Wikipedia info as a refresher ... "On land, the holdover plants included the lycophytes, the dominant cycads, ginkgophyta (represented in modern times by Ginkgo biloba) and glossopterids. The spermatophytes, or seed plants came to dominate the terrestrial flora: in the northern hemisphere, conifers flourished. Glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period."
This means you have all the spermatophytes for possible food, conifers for a bitter tea with vitamin C in lean times (normally, you get all you need from eating fresh meat, fish, shellfish, eggs, &c), and you eat tender little fern sprouts (you can buy canned fiddlehead ferns if you want to taste some).
Humans don't need grasses/grains to have a regular starch supply. In Southern California and Arcadia in Greece, acorns provided an annual harvest. Manioc was grown in South America for its tubers (you know it as tapioca). So the spermatophytes may supply some large harvests.
2) If you want them to land where there's no petroleum, so be it. You're God. But if this is the Triassic, then there must have already have been a Carboniferous, so there's petroleum. They would just have to find it. Unless of course you're a Velikovskyite on where petroleum comes from.
Peat bogs. This is what becomes coal eventually. Look into peat as fuel. Kept the Irish warm for thousands of years.
When they first land, the most immediate local fuel is dried herbivore dung. Look into the use of buffalo chips on the Great Plains.
Coal. Don't see why there wouldn't be any.
Why no firewood? You have conifers. Early pine trees! Junipers! Freakin' sequoias! Cycads have burnable masts, as ginkos have usable trunks.
Which brings us to 3. Building teepees of long trunks, like lodgepole pines, and hides. Big enough dino, you don't have to do much sewing. If I were them, I would be looking for a butte that has to be climbed, with a spring, clear it of most native life, and settle up there. They're not primitives: they know farming. They can domesticate what they like. I can also see them living like Anasazi, but walling off their fields with stone across valley mouths.
They might treat herbivorous quadrupeds like elephants: catch them, use them at least for baggage and draft, feeding and confining them, then when they get too large, release them (or eat them). Archive.org has a pile of late 19th C books on elephant use that may help you imagine their use.
Cynodonts may actually be better choices as permanent domesticated animals.
Stone, wood, and leaves are available for buildings and thatched roofs. Hell, dirt is. I don't just mean adobe: there's rammed earth housing or stuff like pisé. See Cottage building in cob, pisé, chalk & clay. These work in almost any climate, including wet cold Northern Europe. Then there's log cabins, especially double-walled ones in the French style used in Canada.
I also have to note you have "pioneering humans get stranded on a planet" which means they were already set to build a society out of nothing. They will have training to get along without high tech (or they may come from an immoderately stupid culture that thinks nothing can ever go wrong, in which case I don't bet on this lasting twenty years). Where's their farming supplies, including seeds? They won't have much that requires petroleum, unless the first job on landing is to dig oil wells and build refineries. They will have to set up early to produce their own metals.
I would recommend you look at the Foxfire books for how to smelt ores, build wooden turbine water wheels, dry fruits, make soap, and a whole lot else.
If this is a result of a crash, they probably lost all the animals they were carrying as embryos, so you can eliminate that, but having human survivors and absolutely none of the seeds make it through seems implausible, unless the humans got out in the lifeboats while the main ship went confetti. But for pioneers likely to land on an uninhabited planet -- again, I would expect some supplies aboard lifeboats, not just food and water but tools and seeds.
Your 4, "Also, how would the change in the environment bring about the change in the humans?" makes the rash assumption environment would bring about changes. Since modern humans haven't much evolved physically for 15,000 years, I don't see anything radical here. They're going to have to handle only 80% of the oxygen they're used to, and a lot more CO2, but I don't think there's going to be any more difference than with, say, Tibetans or Quechua adapting to the high mountains. The landing generation will miss their normal atmosphere, but the children won't know anything else. They'll probably favor developing more red blood cells for oxygen delivery. Of course, without a pharmaceuticals industry there's going to be a premium on a healthy immunosystem and strong teeth for a long time.
Now, throughout this I've gone along with biological determinism as if this were the Triassic reformed.
I would like to say that if biological determinism isn't what you're doing ... More realistically, the possibility of compatible proteins developing on two planets is close to zero, especially in complex life. Odds are, humans stranded on alien planets will have to sterilize their area and terraform it, at least as far as plants and food animals go, or die.
Conditions? Like temperature and weather? There is no telling what life will exist and its usefulness to us, other than oxygen producing photosynthesis.
If you mean like time travel so that they have to deal with the life forms that existed in the Triassic:
Have: fish, meat
Have Not: fruit, cereal
Need more research: other vegetables. Plants were "low grade" food so digestible stems and leaves would be hard to come by. maybe roots? Look up the lineage of various options and see if they existed back then. A clue is that anything that blooms is not.
What plants that do exist are far from the domesticated food crops. Perhaps necessary vitamins are not available: no citrus fruit to keep the scurvy away. No brown rice, ...
They could build vats to act in the same way as a sauropod's stomach, a more extreme form of modern cow's stomachs. Ferment the plant material to break up the indigestible woody parts and somehow process that into something nutritious to us. Maybe cultivate micro-organism like fungi to then eat.
The people might end up as obligate carnivores with hard-to-produce supplements to get enough essential substances.
I got this from a book called The Lost World by Arthur Conan Doyle.
Because most hostile creatures from that time period were pretty large, you could live in caves with entrances just large enough to fit a human.
You could get food by setting up traps that are essentially hidden pits with spikes in the middle. This would be enough to catch some of the more soft-scales animals.
Also, it would not be too hard to figure out what plants are edible by observing what herbivorous dinosaurs eat.
Edit: The only immediate change I could see this bringing about in humans is improving their dexterity - they would still occasionally have to run away from someone. Also, in the long term, it might bring about adaptations that allow humans to eat a greater variety of plants and animals from that time period.
