1. Create a subfolder under this path;
2. Use the folowing three lines to indicate the order of the title, which will also shown in on Homepage of the left hand-site of the website. 
---
sort: [index]   
---
# First title

Note:  [index] is a number(order) like, 1,2,3,...; For example, For the first title
---
sort: 1   
---
# First title

3. For second or third subfolder, repeat step 1 and step 2 in the corresponding subfolder, then you have the sub-subfolder and sub-subsite.