It's a setting in your phone that you can turn on. it creates a WiFi point from your mobile that others can join so they can use your phones mobile data.
With a mobile hotspot, you can connect up to 10 mobile devices via a 4G LTE smartphone. After a few quick steps, the phone creates its own secure Wi-Fi network for your devices to join. There's no need for a USB cable, and multiple users can share your phone's mobile data plan at once.