@sidjohn1 gave you the short answer and the simple solution, but if you’d like a few more details, see the community FAQ. (The thread title is a clickable link).
To boil that down: all certified zwave devices will work at what the zwave specification calls the “basic” level: on/off/dim for a single endpoint. But any advanced/optional features may require custom code.
So straight out of the box, a device like this
Might only expose the first socket to SmartThings. (Or might turn on all the sockets together rather than individually, depending on how the manufacturer interpreted “basic”).
And a device like this, which is a handheld remote,
Might not work at all straight out of the box, because the remote itself can’t be turned on, and it uses advanced features for the information that it sends to the hub to control other devices.
So both certified zwave, both nice devices, but they don’t work out of the box with SmartThings because their functionality depends on advanced commands.
They can be made to work with custom code, one reason power users really like SmartThings, but that doesn’t meet a plug and play requirement.
As @sidjohn1 suggested, stick to Devices on the official “works with SmartThings” list, and everything will be easier. 