You can create sub-folders for preset folders and for your custom folders.
Option 1: Select Folder and Click the Edit Icon
Go to the Documents Mgmt page.
Click the edit icon (pen symbol) next to the folder name. Select Add sub-folder.
You are taken to the Add Folder interface. The Parent Folder is preset based on the contextual link. Add the name for your sub-folder to the Title field.
Click Save.
Option 2: Click the Add Folder button
You can also add a sub-folder directly by clicking the Add Folder button. Select the folder name from the Parent Folder, and then add your folder name to the Title field. Click Save.