How do I show where each reference goes?

By marking areas on the base image. In Canvas AI, press “Mark reference areas” on the base node and draw numbered rectangles: Reference 1 goes in Area 1, and so on; with no references, the areas show where to apply materials. In the instructions you can type # to mention an area. In AI Chat, tap the base thumbnail to open the area editor.

Areas are a guide for the model, not a mask: they don't guarantee the rest of the image stays untouched, and they count as one more image. To change just one area precisely, use “Retouch” in the Nodes image editor.