A 4x4 Field in Pygame

[Windspar]

You need to go back to the beginning. You miss understood.
Decide on a boiler plate. Then add code.
1. main loop handles events, drawing, and renders its to screen.

[metulburr]

You are not drawing anything in the main game loop. You need to blit inside it to keep drawing the background every frame.

1) indent the pygame.display.flip() to inside the while loop
2) Put your screen.blit just before that in the while loop.