To use the Invisible, Inc. Mod Uploader it must first be installed in your Steam Tools.

To access the Steam Tools, mouse over LIBRARY in the main Steam menu bar. Select the "Tools" item near the bottom of the dropdown list.

Find the "Invisible, Inc. Mod Uploader" in the new list that appears. Double click on it, or right click and select "Install" from the drop down menu.

Run the Invisible, Inc. Mod Uploader from the Steam Tools Menu. It must be installed first (see above)

A window will appear with ADD, DELETE and REFRESH buttons.

The ADD button will bring up a new window where you will enter your mod data.

• Update Data - The folder containing all the files of your mod.
  
• Update Preview Image - An image that will be used on the Steam Workshop page to identify your mod.
  
• Update Details - The text that will appear on Steam to describe your mod.
  
• Tags - select what kind of mod this is, either a language pack or a game content mod.
  
• Visibility - select who can see your mod, Public, Friends Only, or Private.
  
• Publish Button - Once you are ready, this will upload your files to Steam.

The DELETE button will remove your mod from Steam. Subscribed users will have to resubscribe if you post the mod again.

I've never pressed the REFRESH button. I can only guess at it's function. Use at your own peril.