I'm learning InDesign and I've been doing tasks from this book and for some reason, now when I go to use my rectangle tool, it is drawing an octagon or a diamond - everything but a square. I definitely have "Rectangle" not "Polygon" tool selected. Is there a setting somewhere I've changed that is causing this? Thanks.
Sounds like you might have enabled corner effects with nothing selected, making it the default. With nothing selected, go to Object > Corner Options ... and reset to regular corners.
Ta da! Thanks!