If you have a Wifi adapter on a Windows computer, after you connect to a Wifi service, you can easily turn your computer into a Wifi Hotspot, using a program called Virtual Router, download from virtualrouter.codeplex.com
The software is simple, install it, run it, give it a SSID and password, done.
Note: If you only have a wired connection, this won't work, you need to have a Wifi card to be configured as a hotspot device.
If you have just a single Wifi adapter, this is perfect, you connect to a Wifi Router, then make your PC a hotspot gateway.
If you have a Cellular aircard, then treat it like a wired connection, turn on the Wifi, then run virtual router to make the wifi a hotspot.