So, generally speaking, first religion of the Turks was woven around three pillars: Ancestors, Sky and Iron.
Ancestors were sacred and they constituted something like a “souls soup”, when someone died, he became ethereal, and when seven generations passed or nobody remained to remember their laments, they joined “Yer-sub”, “Earth-Water”, with all other nameless and shapeless souls. They could be dangerous when angered and everything in the nature was sacred because souls of the ancestors were the main source of life within everything; everything had a soul, part of this giant “soul soup”.
Sky was the main source of creation and holyness, both called “Kök” and “Tengri”. Gök in Turkish means “sky”, which used to mean “blue” in older times, and “kök” still means “root”. Tengri is the personification of the Sky, but there are examples of this word used solely to mean “sky”, not neccessarily a deity. But when you said “Kök Tengri” (Gök Tanrı in modern Turkish) it directly referred to the main Turkish deity, “Sky God”, and the Turkish noun meaning “god” derived from the word Tengri. Lesser deities, all affliliated with Tengri, sometimes, in certain pantheons, took names like Ay Tengri, Kün Tengri. (Moon God, Sun God). In Altaic and Göktürk pantheon, there were deities such as Ülgen, Ayzıt, Umay; they were not the ultimate source of the creation but perhaps the avatars of Tengri. Yet, it is clear that all Turkic pantheons were polytheistic.
Iron was sacred, it could ward off evil spirits and would bless people. A warlike nation, Turks valued iron above all as expected, because it was iron allowed Turks to survive the harsh conditions of their region. Almost all ancient Turkic rulers have dynastic mythologies regarding descending from a blacksmith.