Good morning can someone do tutor me on my iMac desk top how to use the FaceTime.

Hi diosdado112,

Welcome to the Apple Community.

Re: How to use my FaceTime on iMac Desk Top

You need to be connected to the internet to make FaceTime calls

and the Apple Support articles (links below) can guide you on what you need, and how to get started.

NB: Many of the articles are for Monterey (MacOS 12)

(if you have a different MacOS installed, for accuracy, you can check / change the MacOS at the top the articles)

See FaceTime requirements – Apple Support

How to: Change Settings preferences in FaceTime on Mac – Apple Support

How to: Choose a camera or microphone for FaceTime calls on Mac – Apple Support

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Check you are signed in to your Apple ID on your iiMac

Sign in with your Apple ID - Apple Support

To set up FaceTime on your Mac :

Sign into or out of FaceTime on Mac – Apple Support

How to: Make calls in FaceTime on Mac – Apple Support

How to: Answer calls in FaceTime on Mac – Apple Support

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Troubleshooting if needed:

What to do:

If you can't sign in to your iMessage account or FaceTime on your Mac - Apple Support

If you use FaceTime and iMessage behind a firewall - Apple Support

If FaceTime isn't working on your Mac – Apple Support

(FaceTime may not be available in some countries or regions).

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More support, if needed:

Online FaceTime User Guide:

(Click on Table of Contents at the top of the linked webpage, to see topics, leading to detailed articles)

FaceTime User Guide for Mac – Apple Support

The FaceTime Support Team's Website:

FaceTime - Official Apple Support

or

See a list of Apple phone numbers around the world.

Contact Apple for support and service - Apple Support 

All the best :-)