Overview
Though Humans are as varied as the world's climates, there are no sub-species of Humans. Their cousins, the Neanderthal, were wiped out ages ago, when Giants still roamed the world and settled it as their own. Ever since, the differences between Humans across the world has been solely cultural, not biological. These differences in cultures, beliefs, and societies make Humans one of the most diverse Kith in Aeries by far, rivaled only by the merchant-savvy Hill Unknowns.
Humans are just getting their footing in the world of empires. While Elves, Dwarves, and many more Kith can claim thousands of years of ancient kingdoms, Human-led kingdoms are a relatively novel idea. It was only after the Rage of Demons thousands of years ago were Humans given the chance to be on equal standing with their magical peers. However, Humans have often been very influential in changing the history of the world.
Physical Description
To break the in-universe suspension of disbelief briefly: we're all Humans, we know what Humans look like and what they can look like. It's basically that. Feel free to get even crazier with it, like some Humans in some place having naturally blue hair, or extra hairy backs. Just make 'em Human.
Society
Human societies are as varied as the rest of their traits. In Chult, Human Chultans are mostly settled in the port town of Nyanzaru, having escaped the destruction of their ancient home deeper in the zombie-infested jungles of the island. They have a plutocratic government and wear lighter clothing to account for the warm and humid weather. In Vampyr, Humans act as a middle-class to the caste system of Intelligent Undead - Humans - Unintelligent Undead and dress in warmer clothes with darker hues. In Dolmenwood, Humans are the main practitioners of the Drunish faith, a mysterious and closely guarded Druidic cult that worships ancient Dolish gods.
Human society often has a history of overcoming oppression, such as the Dolish Humans and their several wars with the Goatmen of Dolmenwood that eventually culminated in both a peace treaty held to this day, and the mass migration of Humans to what would eventually become the Angshire Kingdom, one of the first major Human empires.