The idea is to display the first 25 letters of the alphabet. The code below shows the letter a to show what I want to do.
Thank you.
Fabrice

\starttext

\startMPcode
  for i=0 upto 3 :
      for j=0 upto 3 :
          draw unitsquare scaled 4cm shifted (4*i*cm,4*j*cm) ;
      endfor ;
  endfor ;
  for i=0 upto 4 :
      for j=0 upto 4 :
          label.llft("A", (4*i*cm,4*j*cm)) ;
      endfor ;
  endfor ;   
\stopMPcode
   
\stoptext