Official Apple video shows you how to use the Walkie-Talkie feature on the Apple Watch

After installing watchOS 5, make sure that your watch is set to make and receive FaceTime calls. Adding a Walkie-Talkie buddy requires you to press the "+" button and tap on a contact. Once that person accepts your invitation, the box carrying that contact's name turns from gray to yellow. To engage in a conversation using the feature, open the Walkie-Talkie app and toggle the switch to "available." Then, select a person to chat with. Wait until the watch shows that you have "connected" with the other party. Once that takes place, press on the "Talk" button to say something, and let it go when you're done talking. The person at the other end of the conversation will hear what you are saying as you say it.

The Walkie-Talkie feature has several modes. If you don't toggle to "available," you will receive a notification if someone tries to contact you, asking if you'd like to talk. In Silent Mode, you'll hear chimes and the other person's voice. In Theater Mode or Do Not Disturb, you will be unable to use the Walkie-Talkie feature.

If you are more likely to understand these directions by seeing them in action, Apple has released a video that shows you what to do step-by-step. You can find it at the top of this article. You can also head over to the web page that Apple created for the Walkie-Talkie feature by clicking on the sourcelink below. For now, we're "over and out."

source: AppleSupport