In most browsers, you can drag and drop files from your
computer onto the form above. Enter your name and click
"Upload" to watch the progress bar.
Every upload will fail because the server (in this case,
GitHub), doesn't accept form submissions.
I suggest adding large files (> 1 MB) or they tend to
upload too quickly and you can't see the progress
notification.
If you add too many files, the upload button will scroll off
the bottom of the list. Don't do that.
Internet Explorer (except version 10) does not support drag and drop or progress notifications. You can still add files one at a time with the file picker, but you won't see a nice progress bar as they upload.