The specific operation method of folding a rectangular piece of paper into a triangle is as follows:

1. First, prepare a rectangular piece of paper of any size.

2. First, fold the paper in half from the middle, as shown in the figure.

3. Fold a corner onto the folding line folded in the previous step, as shown in the figure.

4. Then fold the paper as shown.

5. Take the next step and further fold the paper.

6. After completing the above steps, we will find that the triangle we want has been completed.