Making your own clippath shapes
Making your own shapes is pretty straight forward.
Start with a zone (usually a text zone) and give it a background color:
On the left, in the Positioning tab > Clippath, you'll see an area for making your shape. Click into it a few times and create some clippath points (you can also click one of the default shapes above and start with those points). Your new custom shape is in pink, and the points are purple. Note how the zone you made (in step 1) changes shape when you drag points around.
Maybe you want a shape to fit a particular area on the card. You can do that by looking at the card preview and moving the shape points to match. Here's a rough example:
Finally If you want to access a shape in other layouts you can give it a name and hit the save button and then you can access it from any layout.
Tip: If you ever want to clear the clip path shape, look for the little X.