how can I open my Mac camera

What do you mean by open your Mac Apple ID?

To use the camera on your Mac, just open an app that uses the camera, such as Photo Booth or Quicktime and select the Camera form the camera options.

What exactly are you trying to do?

Is your camera on your Mac not working?

Please see this link and follow the instructions provided

If the built-in camera isn’t working on your Mac - Apple Support