The grid is a tool where a grid is displayed on the camera screen, making it easier to orient the desired photo to the horizon or to create portraits. You can choose between a square or a 3x3 grid.

Android 10 (One UI 2.0)
Step 1:  Open the  Camera -App
Step 2:  Open the  Settings
Step 3:  Enable or disable  Grid lines
  1. Open the Camera-App
  2. Open the Settings
  3. Enable or disable Grid lines

Samsung Instructions