To open the workshop, you can go to the main menu and click this button: Or, you can also use Steam to navigate to the workshop.
How do I download workshop items after subscribing? If you no longer want an item or mod in your game, you can simply unsubscribe and Steam will remove it. This process works in lieu of downloading or installing individual items from the Steam Workshop. If a game supports Steam Workshop, simply subscribe to it to access its stream of modded content. To activate a mod, simply tick the little checkbox on the left of a mod name in the list and click Apply. Available in the sense that they’re downloaded and copied into the InstallationFolder\Mods. Open the Game Launcher -> Mods window to see the list of available mods.