RE: POBphotocontest New Round: RULE OF THIRDS

Cool! Then you have learned something new!
You can also do this afterwards with cropping your photo with an editor.
But doing it while shooting saves you time.

It is called camera grid. If you have an android phone with the Google camera app you can check out this instructuon video:
https://www.techrepublic.com/videos/how-to-enable-the-camera-grid-in-the-google-camera-app/