Sharing your internet connection with others through wifi, is easy. follow the steps and your Mac will emit a wifi signal.
Step 1: Open System Preferences.
Step 2: Open Sharing, in Internet and Wireless Section.
Step 3: Select the Option of Internet Connection You Have on the Computer.
I use ethernet connection. Any of the options on the list still work.
Step 4: Select the Wifi Option Below.
Step 5: Then Go to Wifi Options and Set the Password.
Step 6: Then Tick Internet Sharing Option, on the Left Side.
来源：http://macintosh.wonderhowto.com/how-to/setup-wifi-hotspot-your-mac-0138193/