Setting your cell phone up as a hot spot and piggybacking on its Internet connection, a feature known as tethering, can be quite useful if you need to get online using a device that can't access the cellular data network. You do, however, need to keep a close eye on how much you download when doing this, to avoid unexpected overage charges.
Tethering enables your other devices to get online through its cellular data connection and therefore counts against your data allowance. To avoid nasty surprises on your next phone bill, check how much data you have left before you start, keep your browsing and downloading to the bare minimum and only use the feature when absolutely necessary. Depending on your cell phone plan and the provider you're using, activating the tethering feature may cost extra by itself, even without counting possible data overage charges. Check your data plan and contract or get in touch with customer service for more information.