To download and use icon packs with Steam Workshop, subscribe to the Workshop item through the Steam Workshop page, and start (or re-start) Decent Icons.

You should see this window on startup:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547205850
Once your Icon Pack(s) are downloaded, this window will close automatically.
You can now use your icon pack by right clicking on an icon, and choosing Configure Icon:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547206923
All your downloaded or created Icon Packs will appear here
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547207775
Simply click the image you wish to use and click "accept" or "save and close".
The search feature will search for tags the pack creator set up for your icons. Search the title of your game to see all images tagged for that game.





To create a custom icon pack (either for personal use or uploading to the Steam Workshop), you'll need to use the Steam Workshop Utility.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547210216
Now click Create in the Top Right corner, and choose Icon Pack from the dropdown.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547211267
Fill out the form here. Note: You CAN change this information later.
Once the icon pack is created, select it from the left hand side.
Now you must fill the icon pack's folder with images.
Select View Folder:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547213047
This will bring you to the folder in Windows File Explorer.
By default there will be a single file called "info.txt" which contains the information you filled out in the form earlier.

Now copy + paste the images you want to use into this folder. .JPG and .PNG ONLY! Once you're done, hit Refresh in the Workshop Utility.

You should now see all your images listed.

Tagging
To allow users (or yourself) to conveniently search for relevant icon images from the Configure Icon window, you need to manually enter tags for each image.

To begin tagging images, simply click on an image you wish to tag:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547216611
Now begin entering tags for the icon. Press enter to add a tag, and once finished, click Save Changes.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547218343
Repeat this for each icon until all icons have atleast 1 tag.

The last step before publishing is to add a preview image, which will be displayed as the thumbnail in the Steam Workshop.

To do this, simply copy+paste the image you want to use as your thumbnail into the icon pack folder, name it exactly preview.jpg, and click Refresh
THIS FILE MUST NOT EXCEED 1MB OR YOUR UPLOAD WILL FAIL
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1547221058
You should see the preview image, and the text "Preview image found!", as shown above.

You're finished!
You may now hit Publish to publish your icon pack to the Steam Workshop.

To publish an update to an already existing workshop item, simply click "Publish" and selecting the pack you wish to update.