The original
Empire of the Petal Throne RPG - available in various affordable reprints - remains a great introduction to the setting. It is weird, but not impossibly weird, and Prof. Barker explains the idea
very clearly. In fact, EPT is also a clean, understandable OD&D variant written by someone who obviously had experience writing college textbooks, skills Gary and Dave obviously did not possess. The rules are not ambiguous, and they are presented quite logically. For extra insight, check out
Fight On! magazine for splendid, play-friendly EPT content and advice.
This thread on the OD&D discussion forums are highly recommended, too.
On its own, EPT starts your characters as lowly foreigners trying to earn money via dungeon-delving and completing missions for local potentates as disposable forces, making it the definitive migrant worker RPG system. You can then graduate them to wilderness play, warfare (there is a great skirmish game hidden in the combat rules), diplomacy, and whatnot. You learn about the world and its peculiarities gradually (although often at your own expense, impáling stákés included)
I never ran
proper EPT, but the City of Vultures described in various issue of Echoes From Fomalhaut is very obviously a homage to it, and you could easily use that stuff in an EPT campaign with a few changes. Otherwise, published adventure materials are pretty scarce;
The Tomb-Complex of Nereshánbo is a functional but not terribly outstanding dungeon adventure, and Judges Guild's
The Nightmare Maze of Jigrésh is considered weak. Most published Tékumel material lies in the deep "culture-gaming" territory, and perhaps not of much interest to D&D players.