Here are situations where Internet Sharing is particularly useful:
You don’t own a wireless router – no problem, let the Mac become one
There is only a wired internet connection (ethernet) available, and you need to get a wireless-only device online, like an iPad or MacBook Air
You’re at a location that charges internet access per device, rather than a flat rate for all devices, this is fairly common at hotels and airports
Skirt the connected device limitations of Personal Hotspot (iOS) and Internet Tethering from mobile phones
It’s easy to set up, let’s get started:
We’ll walk you through the process of setting up a secured wireless access point, broadcast from an internet connected Mac to be shared with other Macs, PC’s, or iOS devices.
Connect the ethernet cable to the Mac
Launch “System Preferences” from the Apple menu and click on “Sharing”
Click on “Internet Sharing” from the left menu
Select the pull-down menu next to “Share your connection from:” and choose “Ethernet”
Alongside “To computers using:” check the box next to “Wi-Fi” or “AirPort” (name depends on OS X 10.7 vs 10.6)
Next click on “Wi-Fi Options” and name the network, and then click to enable security/encryption, and then type in a WEP key as the wireless password
Click “OK” and confirm that you want to start internet sharing
You’re done. Your Mac is now broadcasting a wireless signal that can be picked up by any other wi-fi enabled devices. Connecting to the Mac’s shared internet connection is now the same as connecting to any other wireless network, find the wifi access point name you set, enter the password, and you’re online. The network is relatively secure thanks to the WEP password you set, if you forgot that password you just have to disable security and re-enable it to set a new one.