Using a mobile device, such as a smartphone or tablet, to provide Internet access to other Wi-Fi enabled devices is referred to as tethering. The act of tethering your smartphone or tablet creates a Wi-Fi hotspot, which other devices can connect to like any other Wi-Fi signal. Many smartphones have the tethering capability built-in, while others require a special app or don't have it at all.
Are there charges?
For the most part, mobile phone service providers only charge for tethering in the form of normal data usage. However, a few charge a monthly fee to allow customers to use their smartphone for tethering. Some people get around this by rooting their phone, but this is technically not legal and is considered a breach of contract. Check with your service provider for specific details.