All Prison Architect Mods follow these simple steps:

1. Subscribe on steam to the mod you want to use.
2. Allow the mod to download.
3. Open your game to the main menu screen
4. Go to the Extras section on the main menu
5. Then go to the Mods section.

Here you can see all the mods on your computer for prison architect.

6. Use the little check box on the right to select the mod you want.
7. Click the apply button at the bottom.

Your game will reload/flicker and then show the mod in the active section.
Any prisons you make will use the mod and any you open will allow use as well.