Diamond Rosette
The two larger pieces are for the large diamond and need to be glued together. Use liquid glue for this. Overlap the end folds of each piece with the end folds of the other piece. You will need to stand them on end and form a circle to do this. The smaller piece needs the two ends glued together, again standing on end and forming a circle.
Press the circle flat by forming a cone with the bottom and pressing the cone flat. Then glue the diamond to the top of the accordion folds with a glue gun.
Put the smaller rosette on the larger and glue together with a glue gun.