My copies are all the same

You scattered thirty rocks and got thirty identical rocks. Nothing is broken, which is why nothing tells you about it: identical copies are a perfectly valid result, and the graph cannot know you wanted otherwise.

Nothing is varying them yet

Instancing places the same shape at every point. Unless something feeds a different number to each copy, every copy is the same.

Wire a Random Value into the Scale of your instancing. That is usually the whole fix. Rotation is the other one worth adding, and for anything with a flat top a random turn does more for the look than size does.

You varied it, and they still match

The usual cause is that the varying value is being read once instead of once per copy.

Only a few things read a different value for each copy: the instancing node itself, Transform, Set Material and Color Ramp. Wire a Random Value into something else and it will connect, the box will grey out, and every copy will quietly get the same number.

If the variation has to reach further than that, vary the instancing and let the shape follow, rather than trying to vary something deep inside the shape.

They vary, but the same way every time

That is the seed doing its job. The same seed gives the same arrangement on purpose, so a graph you export behaves the same way twice.

Put the seed on a knob and turn it when you want a different draw.

They vary too much

Random Value has a smallest and a biggest, and the gap between them is doing all the work. Narrow it. Real scatters vary less than people expect, and a range of about half to one and a half already reads as natural.