1- Open Silhouette studio. Click on the shape tool and select the rectangle .
2- Draw the rectangle and add the score line.
3- Insert the design you want to use as a stencil.
4- Resize the design to fit the front of the card base.
5- Click on the offset icon. Create an offset.
6- Select both the offset and the design.
7- Adjust the design and offset so it has an edge that touches the top, side and bottom of your cards edge.
8- Double click on the card rectangle. this will bring up the point editing tool.
9- Add a point as each section where your design and offset touches the edge of the rectangle.
10- Delete the top corner and bottom corner node.
11- With everything selected right click and weld.
12- Select both the car that now has a shaped edge and the design. Click on modify tool and then subtract.
13- The design will be cut out of your card base and as you can see below the card now has a shaped edge with a stencil aperture.