Creating custom polygons

I need to create ellipse and a half moon shaped stimuli using the custom polygon function in the builder. I am having a hard time figuring out how to start selecting points to start with. Is there a tutorial available on creating custom polygons anywhere?

The shapes I’m trying to recreate can be seen below.

For the ellipse, you should be able to use a circle with a larger horizontal size than vertical.

For the half moon you could use a circle and then hide the bottom half with a black rectangle. Alternatively, you could use a custom list of points (removing the bottom half of my circle points from the following thread).