sim card

I want a new tablet but no stuck to any brand and need to know if a Sim needs to be installed if there is a sim tray/ slot? I will only use a tablet for local and wifi - do not need data/ roaming service but am wary of tablets which would not work without a sim. Any advice would be a great help

Excuse my ignorance, but I just picked up a refurbed Samsung GS tab S and can't connect to WIFI. It's saying I need a SIM card (didn't need one for used iPad). I just want to connect to WIFI, not use this thing as a phone. Do I need a SIM card just to use this as a WIFI device?