You can use the Corner Options command to quickly apply corner styles to any path. Available corner effects range from simple, rounded corners to fancy ornamentation.
Note the following:
If you’ve obtained plug‑in software that adds more effects, the Corner Options command in the Stroke panel can include additional shapes.
Corner effects appear on all of a path’s corner points, but never on smooth points. The effects change angles automatically when you move a path’s corner points.
If a corner effect significantly changes the path by, for example, creating a bulge inward or outward, it may affect how a frame interacts with its contents or with other parts of the layout. Increasing the size of a corner effect may push an existing text wrap or frame inset farther away from the frame.
You can’t edit a corner effect, but you can change its appearance by changing the corner radius or modifying the stroke.
If you applied corner effects but can’t see them, make sure that the path uses corner points and that a stroke color or gradient has been applied to it. Then increase the Size option in the Corner Options dialog box, or increase the stroke weight in the Stroke panel.