The mobile hotspot feature on your phone allows you to share its data connection by creating a Wi-Fi network. Other Wi-Fi devices, such as Laptops, Kindles, etc can then access that Wi-Fi network and use the phones data network. The procedure is referred to as creating a mobile wireless hotspot.
To set up a mobile hotspot with your phone, either check your manual or do a Google search other particular model you have.
Here's how you set up I my Samsung 9 hotspot.
When the mobile hotspot is active, you see the Hotspot Active notification icon, similar to the one shown. You can then access the hotspot by using any mobile device that has Wi-Fi capabilities.