In what order am i supposed to watch pic related cuz i think it has four installments but i dont know where to start.
You can watch either one without the other but if you want to go in chronological order watch rail gun first
I1 -> R1 -> I2 -> R2 (-> movie)
and you're done.
Wrong. You're supposed to read the Railgun manga and then watch Railgun S episodes 2-16 for glorious suffering and terrorism, then drop it before the next episode preview. Index anime is optional, but reading the novels is mandatory.
STUDY overlaps with 3 stories and Hyouka? How does that work when Mikoto has a consistent presence in those arcs?