How to use Workshop Items?
 

I downloaded a couple of items in the Steam Workshop. They appear in my list. It says they are downloaded, but when I click to "install or re-install" them, it just blinks. Is there something I'm missing? To make the items (3D Models) show up?

Sounds like you are doing the steps correctly. Subscribe to the item in the Workshop section of the game. Go back to the Main Start Screen. Open Workshop Central at the bottom of the screen. Click the subscribed item. Download it. Then above that, the install button.

For stadiums, for them to show up in the game, the historical ones from silvam14 should load automatically in a historical game since the era_ballparks file looks for them. For the others, you need to manually navigate to them and load them/assign them to a team. See this thread:

https://forums.ootpdevelopments.com/...d.php?t=362674

The image with the park showing is where you can manually assign a stadium to a team and that's probably the easiest way to see if you have the downloaded parks.

Alternatively, if you want to check via file explorer, go to the Main Start Screen, hit the Troubleshooting tab, click "Open file with customizable data", then navigate to ballparks/models and see if you see the parks in there that you expected to download. That's where the Workshop put stadiums.