Trions looked identical to humans and could survive in similar conditions.
Trion society was for a long time constituted almost as a caste system, with much of the power and privilege the sole preserve of the ruling Clans. (TV: Planet of Fire) Different castes lived in different parts of the cities. (PROSE: Lords of the Storm) There were also shantytowns around the palaces. (PROSE: Zeitgeist) These clans were later overthrown, but the later regime was overturned, returning the Clans to power. (PROSE: Turlough and the Earthlink Dilemma)
Trions on the colonies had different traditions. On Sarn, they worshipped the fire god Logar, which was actually based on the memories of Trion vulcanologists. Those with the Misos Triangle were known as the Chosen Ones. (TV: Planet of Fire)
The Trions were a reasonably advanced species, having space-faring capabilities and energy weapons. One Trion seemed completely unfazed by the fact that the Doctor's TARDIS had a dimensionally transcendental interior. (TV: Planet of Fire) Turlough was familiar with transmats. (TV: Mawdryn Undead)
The Clansfolk were evolving "out of the jungle" when the Laima arrived on the planet. Early on, the Laima fed on the Clansfolk, but eventually stopped and considered that time of their existence to be barbaric. (PROSE: Turlough and the Earthlink Dilemma) Early in their history, the planet was invaded by the Tractators, an experience so horrific that for generations to come, an ancestral memory of it would be triggered at the sight of one. (TV: Frontios) The Laima left the physical universe, leaving behind the Slots who named the planet "Trion" after the three great civilisations. The Clansfolk took that as their name. (PROSE: Turlough and the Earthlink Dilemma)
The Trions had had colonies planets for centuries. (PROSE: Lords of the Storm) This included Sarn, Darvey, Verdon, and New Trion. Some of these colonies, like Sarn, were abandoned over time. According to Turlough, the Trions had undercover agents on every civilised planet, including Earth. (TV: Planet of Fire)
During Turlough's youth there was an uprising against the Clans, led by Rehctaht. The Clansmen were deposed, their families broken up and sent to other planets - some Trion colonies, some not. These political exiles were marked with the Misos Triangle and were watched over by the Custodians. Rehctaht's tyrannical regime was eventually overthrown and the exiled Clansmen were allowed back on their original home. (TV: Planet of Fire, PROSE: Turlough and the Earthlink Dilemma)