Start a FaceTime Session On an iPhone Running iOS 11

FaceTime, a built-in app in your iDevices running iOS 11 allows you to make voice and video calls to your contacts. In order to make a FaceTime call, your iDevice must be connected to the Internet, and the FaceTime option must be enabled and properly configured in the Settings > FaceTime window.
Also, if you’re using the Internet from your cellular service provider, the FaceTime switch must be enabled in the Settings > Cellular window without which your device may not be able to make or receive FaceTime calls.
Once all the configurations are in their correct place, here’s how you can start a FaceTime session in an iPhone running iOS 11:
    Launch FaceTime
    Locate and tap the FaceTime icon from the Home screen (present on the second page of the Home screen by default). This launches the FaceTime app. The first interface of the app shows the logs of any FaceTime calls that you may have made or received earlier, and remains blank if using for the first time.

    Pick the correct tab
    Either leave the Video tab selected or tap the Audio tab from the top. This lets you make a video or audio FaceTime call respectively. Selecting a tab in this step is optional as you can choose your preferred type of call after selecting a contact as well.

    Pick a contact
    In the search field, either enter the name, email address, or phone number of the contact you want to make a FaceTime call to, or tap the + icon from the top-right corner, and tap your preferred contact from the list. This selects the contact and shows the FaceTime options available for them.

    Make a FaceTime call

Tap either the Audio or Video icon next to the contact’s name. This initiates a video or audio FaceTime call respectively. Wait for your contact to answer the call. You can tap the Hang Up icon to end the call when you’re done.

Note: If you do not tap video or audio icon, and tap the name of the contact itself, the video call is initiated by default.