hello,

good question!

You find general information about classes here:
https://forum.processing.org/topic/class

I suggest make a class named Cell and then in setup
define a global 2D array of 11 colums, 11 rows which contains
those cells.

The class would have the properties x,y (position)
width and height and a letter and at least 2 colors (one for background, one for the letter).

search grid here in the forum.

Greetings!