How do I use my iPhone 5S without a SIM card to use on WiFi

You cannot activate an iPhone without a sim. The sim does not have to be

associated with an active cellular account; however, if the iPhone is locked to a

particular wireless provider, the sim must be from that wireless provider.

Ask an wireless provider for an inactive sim (if iPhone is locked to a

wireless provider, ask that wireless provider) or borrow an appropriate

sim from a friend/relative/co-worker for the few minutes it will take to

activate the iPhone.

You will need a sim if you restore the iPhone or update the iOS version.