You cannot create an empty folder and then add files to that folder,
but rather creation of a folder must happen together with adding of
at least a single file. On GitHub you can do it this way:
Go to the folder inside which you want to create another folder
Click on New file
On the text field for the file name, first write the folder
name you want to create
Then type /. This creates a folder
You can add more folders similarly
Finally, give the new file a name
(for example, .gitkeep which is conventionally used
to make Git track otherwise empty folders; it is
not a Git feature though)
Finally, click Commit new file.