I can’t make calls on my Apple Watch. What should I do?

First off, you need to explain what happens when you try? Are you using a GPS only Watch? Is the iPhone nearby when you attempt to make the call? If it is a GPS + Cellular Watch, is the cellular activated with your carrier? If you check the Watch in Control Center, is the cellular connected and do you see a signal? Do you see any errors when you attempt to make the call, and if yes, what are they?