To use a Nikon Coolpix camera as a webcam or main camera for a mobile phone, you will need a few things:

1. A Nikon Coolpix camera that supports the use of a USB cable for streaming video.
2. A USB cable to connect the camera to your mobile phone.
3. An OTG (On-The-Go) cable adapter, if your mobile phone does not support USB connections.
4. A third-party app that can convert the camera’s video feed into a format that your mobile phone can use as a webcam/main camera.

Here are the general steps to follow:

1. Connect your Nikon Coolpix camera to your mobile phone using a USB cable. If your mobile phone does not have a USB port, connect the camera to your mobile phone using an OTG adapter.
2. On your Nikon Coolpix camera, navigate to the settings menu and look for an option to enable video output via USB. This may be called “USB streaming” or something similar.
3. Download and install a third-party app that can convert the camera’s video feed into a format that your mobile phone can use as a webcam/main camera. Some popular options include DroidCam and iVCam.
4. Open the app on your mobile phone and follow the instructions to set up your Nikon Coolpix camera as the video source. This will typically involve selecting your camera from a list of available devices and adjusting some settings like video quality and resolution.
5. Once your camera is set up, you should be able to use it as a webcam/main camera for video calls or recording videos on your mobile phone.

It’s worth noting that not all Nikon Coolpix cameras support USB streaming, so it’s important to check the specifications for your particular model before attempting to use it as a webcam.