What does the upload progress screen actually show me?

You get the usual live stats: how many files are done versus total (something like Files 0/0), how many megabytes have made it up, and your current speed in MB/s, plus a Start Upload control to kick everything off. It's the kind of panel you glance at to confirm things are moving, then ignore while it does its thing in the background. For big uploads the speed readout is genuinely useful for spotting a flaky connection before you walk away for an hour.