For related pages inside the same section follow the same instructions as step 2 of the previous section.
This time, instead of giving the page the system name of "index", give it an abbreviation of what the Display Name will be titled. Click Submit.
When the page is viewed in the cms, it has now been added as a sub-section in the left navigation.
Be aware that the title in the Display Name should not be too long, otherwise, the left navigation display of the text will be bulky and difficult to read.