2. Open the four symbols on the back and find the second plus sign; By the way, this directory is actually a bookmark, just like a bookmark in a word document. When adding an index, it must be on the page to be indexed.
3. Then click the plus sign to add a directory, as shown in the figure below. 4. Modify the directory name, click "Untitled" to modify it and change it to the title you want.
5. Add a secondary directory. Please note that when you click the plus sign again, the default is to add a sibling directory. You need to hold down the title to be moved with the mouse, and move it to the required position according to the cursor symbol, as shown in the figure below.