I figured this out. Go to the mods, in game, and find your mod in the list. There should be a button on it that looks like a download icon. This is actually the button to upload and publish. You then need to edit the title and description for your mod in the steam workshop and set your mod's visibility to public since otherwise it will default to private and no one will see it.

you're not the only one who's had this issue. thank you.