Depending on your plan, you will have different hotspot allowances.
On the Unlimited plan, you can use 5GB as a hotspot at 5G speed, once you reach the cap your speed will be throttled to 2G.
On the Unlimited Max pan, you can use 15GB as a hotspot at 5GB speed, it will be throttled to 3G speed after you reach the cap.
On the 1GB and 3GB plans the data you use just pulls from your monthly plan. However, please note that data speeds will be at 600kbs.