PlateUp! has native mod support built in, mods install with a single click through the Steam Workshop, no extra tools required.
This is the only supported way to install mods.
That's it! Steam handles downloading, enabling, and future updates automatically. When a mod author pushes a new version, your subscribed copy updates the next time you launch.
Some mods rely on other mods to function, a shared library for example. If Steam prompts you to install additional items alongside the one you subscribed to, this is what's happening.
In almost all cases, you should accept these prompts. Declining usually means the mod you actually wanted won't work correctly.
Check Troubleshooting for common install issues, or ask in the Unofficial Modding Discord or the Official PlateUp! Discord, it's the fastest way to get help from people who've hit the same problem.