If you want to use the mobile hotspot that is available with the iPhone 5 you need to make sure you have a wireless plan that adds the tethering package. This can cost anywhere from around $20 or more per month depending on your carrier. If you are sure you have a plan that includes the mobile hotspot features then you can tap on Setting, General, Cellular and then Personal Hotspot and confirm that the devices you want to connect to the hotspot meet the system requirements. If they do, you should be able to connect without any issues.
If you do have issues connecting a device to your iPhone 5 mobile hotspot, even though they have the correct system requirements, disable and then re-enable the mobile hotspot through the Setting, General, Cellular and then Personal Hotspot prompts to see if that corrects the connection. If the connection still isn’t working properly, check to make sure that you have the latest iOS version installed by tapping Settings, General and then Software Update. You can also try resetting the network by tapping on Settings, General, Reset and then Reset Network. If all else fails, restore your iPhone 5 and then try again.