This 'question' has been carefully reworded.
It used to read, "Maximum number of dots in a Braille letter".
The thing is, no letter (or other character) uses more than five dots. If all six dots are present, this signifies an error (the original character has been overwritten).
The six places in the cell, or grid, are arranged in two columns of three.
If you require more details, Wikipedia has a detailed explanation (as you would expect!).
© Haydn Thompson 2018