Welcome aboard. Enjoy the ride.
We look forward to seeing more posts and samples of your work.
We need some more information to be able to help you. Best bet would be to download a sample photo with EXIF data so we know what shooting mode, ISO, shutter speed, etc. you are using?
That's the Nikon software displaying which focus-point was used when the shot was taken. The red box won't appear in your finished image.
When viewing image while using either ViewNX-I, or Capture NX-D, you'll find the option to display the focus point under the "Image" menu (Show Focus Point), or you can use Ctrl+Shift+F to toggle the focus-point viewing feature.