There is a cloud to cloud integration between SmartThings and Tuya/SmartLife. None of this works locally, it is all Internet dependent.
To add Tuya WiFi devices to ST go add device (+), partner, SmartLife and follow the prompts. Unfortunately many devices are not supported by this integration.
There is a workaround to get plugs, bulbs, switches and relays partly integrated. See the following link for details.