Here, I cut a heart-shaped hole into a piece of black cardboard, a bit smaller than the lens diameter, fixed it in front of the lens, and took a photo of my Christmas fairy lights in my backyard. (You can try this with any shape, squares, triangles, stars, butterflies or something else and shoot against some point-shaped lights, the bokeh will take the shape of the notch as long as the notch is smaller than the aperture of the lens.)