First rule of home automation: “the model number matters.“ Even for the hub. Some smartthings hub models can use Wi-Fi, some have to be cabled to the Internet. The model number should be on the bottom of the unit.
In any case, it’s usually best to have the hub out in the open to maximize the quality of transmissions to and from it. If you do need to put it in a locked cabinet, make sure it’s a wooden cabinet or plastic, not metal and not one of those red Chinese lacquer styles, that particular paint has a lot of iron in it. clear glass is fine, colored glass can be a problem.
In no case can you plug another device into the hub for Internet or Wi-Fi, the ports on the back of the hub are unfortunately non-functional. However, if you do have one of the hubs that needs to be cabled, you can run an ethernet cable to a Wi-Fi access point that has an ethernet port on the side if that helps at all.