Linc Davis wrote:
If you're connecting to the Internet via Wi-Fi, you can't share the connection. If you're connecting via Bluetooth or USB, you can share via Wi-Fi.
For instructions see http://osxdaily.com/2012/01/05/enable-internet-sharing-mac-os-x/
BTW - If I select sharing over WiFi, my, MBA says the connection can be shared by either Bluetooth PAN or USB Ethernet. I'm not sure how that would work though.