Hi there, Rachael_O.
Congratulations on your new iPhone 12!
It appears that you're seeing a strange green dot at the top of the screen of your iPhone. You're wondering what it is, and we're glad to help with this.
Status icons and symbols on your iPhone - Apple Support -- Scroll down to "If you see orange or green indicators in the status bar" lower in this article. The green indicator means that either the camera or the camera and microphone are being used by an application on your phone.
iPhone User Guide - Apple Support -- Since there’s many new features with your iPhone and iOS 14, we’ve included the iPhone User Guide for more information.
Feel free to get back to us with any questions or problems you may have.
Take care.