You will need: 15 buttons, glue (best glue gun with three charging), tape and a piece of paper.
On a piece of paper tape the first pieces of adhesive tape, but so that the sticky part is toward you. Attach the buttons on it in the shape you want. Put the glue over them, so that they connect well. Wait for the glue to dry, then peel off the buttons with pieces of adhesive tape. See more details in the video: