Can I use my personal hotspot (on iPhone) to connect my laptop to the internet?

My internet connection is terrible from my Comcast modem and so I turned on my personal hotspot that I have on my iPhone and now I'm using that Wi-Fi for my MacBook.

Will my data usage increase? I pay an extra $10 for personal hotspot on my AT&T bill, so I thought that they won't charge me for using PH because I already have it on my bill…

They are separate services. The hotspot simply allows you to hand out your internet service to whomever. Data charges set you a limit, once you pass it, they reduce your data speed but you can still give out internet.

It will use data, so if you do video streaming or downloading any videos, you may want to keep an eye on your data usage. If you go over the amount they allow per month they will charge you extra.

The T-Mobile plan I have that allows my phone to be used as a hotspot does not charge me extra (like AT&T and Verizon do) if I go over my monthly limit. T-Mobile just slows it from 4G to 2G.