Stock Android has had built-in tethering since version 2.2 way back in 2010, but most carrier-branded devices in the US have the option disabled. Sure, there are root apps and various workarounds, but they can be a mess. If you don't need web access, but want your devices on a local network, you're often out of luck. A new app from well-known developer Chainfire gives you back some control (on some devices), and it doesn't require root.
The app is designed to be simple – just pick a network name and a password, then activate. WPA2 AES + TKIP is always enabled in the interest of security and ease of use.