Sewing a curved edge

Ever have two pattern pieces that are supposed to be sewn together but are actually curved in opposite directions? You wonder how they are possibly supposed to fit together. Sometimes you’ll see this in shaped seams, like a princess seam on a woman’s top that must make room for the bust. Sometimes, in the case of this tutorial, it’s a flat seam (meaning, not convex) that is rounded for visual effect. It’s really not hard to do, and I’ll show you how.