A gris-gris traces back to West African Islamic amulet practice, where a verse of the Quran or another sacred text was written on paper and sewn into a small leather or cloth pouch, a direct counterpart to the hirz and similar written talisman traditions found across the wider Islamic world.
What changed on the crossing
Carried to the Americas through the transatlantic slave trade, the practice merged with West African indigenous traditions and, in Louisiana specifically, with Voodoo and Hoodoo practice, picking up additional material components along the way, herbs and specific curios added to or in some cases replacing the written verse entirely, so the object diversified considerably by region rather than staying a single fixed form.
Who makes one, and its upkeep
A gris-gris is made by a practitioner within whichever of these traditions a person is working, with no single universal recipe given how much regional syncretism shaped the practice, and it is worn against the body, refreshed periodically, and disposed of according to the rules of the specific working it served once that working concludes, much as a mojo hand is, though the two traditions are historically and materially distinct despite the similar function.