Needed materials and tools: milk cartons, carving knife, markers

The first step, first of all, the four sides of the milk box lid removed, as shown in the following picture:

The second step, and then in the wide side of the hole, as shown in the following picture:

The third step, and then the other side of the wide side of the same hole, as shown in the following picture:

The fourth step, and then finally wrapped up! can be placed on the bookshelf books, as shown below: