In order to make a beautiful greeting card, you need to prepare the following materials: a piece of cardboard, a piece of colored paper, scissors, glue, colored pens, and a ruler. These materials will help you create your original greeting card!
First, let's draw a rectangle on cardboard. The size of this rectangle can be decided according to your needs. Then, cut out this rectangle with scissors, and that's the shell of our greeting card. Next, choose a piece of colored paper and fold it into a small square. Fold this square diagonally to form a triangle. Fold the triangle along the midline to get a smaller triangle. Repeat this process until you get a very small triangle. Unfold this smallest triangle into a square. Then, fold this square diagonally to form a triangle. Fold the triangle along the midline to get a smaller triangle. Repeat this process until you get a very small triangle. Unfold this smallest triangle into a square. Then, fold this square diagonally to form a triangle. Fold the triangle along the midline to get a smaller triangle. Repeat this process until you get a very small triangle. Unfold this smallest triangle into a square. Then, fold this square diagonally to form a triangle. Fold the triangle along the midline to get a smaller triangle. Repeat this process until you get a very small triangle. Unfold this smallest triangle into a square. Then, fold this square diagonally to form an isosceles right triangle. Then unfold the isosceles right triangle to form a rectangle. Finally, fold this rectangle diagonally to form a new isosceles right triangle. 
Repeat until you reach your desired shape or size. A simple origami process has now been completed. This process can be seen as a recursive algorithm that repeats the same operation at each step until the desired result is achieved. Recursive algorithms can be applied to many other shapes and designs, such as airplanes, boats, flowers, and so on. Origami is not only a form of entertainment, but also widely used in real life, such as making robots, packaging boxes, artwork, and so on. In addition, origami is also used to study and solve complex mathematical problems, such as geometric and topological problems. Overall, origami is not only fun, but also very practical, it allows us to better understand and apply mathematical and geometric principles. If you want to learn more about the art of origami, you may wish to search for relevant books, or even try folding some interesting shapes and designs yourself!