Hi and thanks for reaching out. My name is William. I'm a Windows technical expert. I'll be happy to help you out today.
Technically, a system folder is a folder that resides outside of the user profile, e.g. C:\Windows... Folders like Documents, Downloads, Pictures, etc are unique to each user account. To create a new folder in the latter, open file explorer > navigate to C:\Users\YourUsername and create a folder anywhere in the tree by right-clicking in a blank space > selecting New > Folder.
if you want to create nested folder (or subfolder), then navigate into the respective folder(s) and perform the same action above.
If you need something with more detailed steps. see: https://www.webucator.com/how-to/how-create-new...