You need to confirm that At&t has enabled the Hot Spot feature for the phone. Ask them if it is included in your current plan. If not, ask what it would cost extra, how much data would be included and confirm how much data could be use before the connection speed is slowed down (throttled). Once setup properly, the hotspot can be manually turned on or off through the cell phone.
I just gave myself a gift of a new iPad mini. I have an iPad Pro, and iPhone using AT&T. I really don't want to pay any extra for the new iPad, as I won't be using the cellular on it much, so wondered if I can use my iPhone as a hot spot and how to do it. Thanks, Peggy