How do I create a folder in a GitHub repository?

Git doesn't store empty folders. Just make sure there's a file in the folder like doc/foo.txt and run git add doc or git add doc/foo.txt, and the folder will be added to your local repository once you've committed (and appear on GitHub once you've pushed it).

TL;DR Use / in the file name field to create folder(s), e.g. typing folder1/file1 in the file name field will create a folder folder1 and a file file1.

Original answer
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. This is because git doesn't track empty folders.

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.