There are several apps that allow your phone to act as a hotspot, including 1-Click Tether, Toggle Wi-Fi, PdaNet, EasyTether and ClockworkMod Tether. All offer free or lite options as well as paid options with more features.
The paid versions of these apps provide unlimited Internet access, while the free limitations include having to reconnect every few minutes or not establishing secured connections. None of the aforementioned apps require rooting your phone, so you will not void your warranty by downloading them. Additionally, they are all easy to use, simply requiring a few clicks with little to no configuration required. However, keep in mind that the best and most reliable way to obtain a Wi-Fi hotspot is to use the built in hotspot app supplied by your carrier.