You can make FaceTime audio calls right from the Messages app on your Apple Watch.
Go to the Messages app at the bottom of the screen, then choose a contact.
You have these options when receiving a FaceTime audio call on your Apple Watch:
Answer the call: Tap , then choose a contact, or tap Add People, then choose a contact.
View a recorded video message: If you don’t answer a FaceTime call, the caller can record a video message, then send it to you. To view it, just tap the notification when it arrives, or open the conversation in Messages later, then tap the video.