FaceTime for Mac is a software tool which allows you to make and receive video calls to the Mac users or on the supported devices using FaceTime. FaceTime is available for Macs running Mac OS X Snow Leopard v10.6.6 or later, iPod touch (4th generation) or later, iPhone 4 or later, and iPad 2 or later (including iPad mini).
But cross verify some other points as well like:
FaceTime may not be available in every country or region
How to troubleshoot FaceTime on iOS Devices (iPod touch (4th generation) or later, iPhone 4 or later, iPad 2 or later and iPad mini), see iOS: Troubleshooting FaceTime
Let’s Verify does your Mac meets the FaceTime system requirements
To avail the facility of video calls, your Mac needs:
OS X Mountain Lion, OS X Lion or Mac OS X v10.6.6 (or later) with all available security updates installed.
OS X Mountain Lion and OS X Lion already include FaceTime. Purchase the FaceTime App from the Mac App Store for Mac OS X v10.6.6 or later.
At least 128-Kbps or better upstream and downstream Internet connection speed because performance may vary according to network throughput.
A built-in FaceTime camera, a USB video class (UVC) camera, an iSight camera (built-in or external), or a FireWire DV camcorder.
To make HD video calls, you need a built-in FaceTime HD camera and a 1-Mbps upstream and downstream Internet connection.
To receive HD video calls, you require a supported Intel-based Mac. For a complete list, see this article.
For the voice input, you can use a built-in microphone, or connect an external microphone to your computer’s audio input port.
Otherwise, as an alternate, you can use compatible Bluetooth or USB microphone or headsets.
In case there are multiple cameras or microphones attached to your system, use the Video menu to choose the camera or microphone you want to use with FaceTime for Mac.
Activating FaceTime for Mac
Your Apple ID is the key to register and use FaceTime. FaceTime registration validates your Apple ID and email address then you can use FaceTime.
If you are unable to activate FaceTime, follow the following tips:
Use a valid Apple ID to Sign in to FaceTime for Mac. Once the email ID is validated for use with FaceTime, other FaceTime users can connect to you using that email address. Try these steps if you encounter issues while registering or using an Apple ID for using the FaceTime:
Make sure that you have the Internet access.
Verify that you’re using a valid Apple ID at appleid.apple.com. This site also can be used to create an Apple ID or reset your password.
Check that your email address is verified in FaceTime > Preferences.
If FaceTime > Preferences shows your email status as “verifying,” follow the instructions written in the verification email to complete the process.
Toggle FaceTime off and on in FaceTime > Preferences.
If still you can’t Sign In, follow the instructions in FaceTime, Game Center, Messages on OS X: Troubleshooting Sign in
Troubleshooting FaceTime for Mac
Using the FaceTime app, you can make FaceTime calls to the other FaceTime users whose contact information is in Contacts. You allowed adding contacts and editing contact information in either FaceTime or Contacts. You may use a phone number or email address to make a video call.
Try the following instructions if you encounter issues while making or receiving FaceTime calls;
Ensure that FaceTime is enabled in FaceTime > Preferences.
If the issue still persists, or you receive the message “Waiting for Activation”, try toggling FaceTime off and then on.
Make sure that the Date, Time, and Time Zone are set correctly:
Otherwise from the Apple menu, choose System Preferences > Date & Time > Date & Time.
Or enable “Set Automatically”.
Click on the Time Zone tab and confirm the closest city is correct.
Verify that there is an active broadband Internet connection on both parties.
See Mac OS X: Troubleshoot a cable modem, DSL, or LAN Internet connection errors.
For necessary ports to open in firewalls, security software and routers, consult using FaceTime behind a firewall.
Use standard Wi-Fi network troubleshooting to resolve interference and other issues, if you experience issues using a Wi-Fi network.
Verify that the phone number or email address being used is the correct one to activate FaceTime.
Make sure that you are using a valid Apple ID at appleid.apple.com. You can also use this website to create an Apple ID or reset your password.
Make sure that both parties have installed the latest software updates for their Mac machines and/or device.