My teacher already has all assignments, slides, and units prepared - is this normal?

I feel like I’m doing something wrong because I’m doing so little so far. For the first two weeks of my placement I’m supposed to just observe and “learn the ropes” as my supervisor put it. So far, I’ve discovered that the teachers in this school all collaborate throughout the years to create assignments and slides and units and stuff for their classes and grade levels. Basically, everything for the whole year is already made, and I’m allowed to make small tweaks if I want but am expected to stick to their pre-made units and just administer and present.

Is this normal for a student teacher? I really have no idea but I feel like I’m doing something wrong. At the same time I don’t want to disrupt the system that these teachers already have in place.