The genetic code is a messenger RNA (mRNA) code read in three-letter blocks (codons) in the 5'  3' direction.

The layout of the code above is the standard 4 x 4 x 4 presentation. To read the mRNA codon 5'-ACG-3' :
Read the A across the first-letter block on left-hand side of the table, then
Read the C down the second-letter column across the top of the table, finally
 Read G as the fourth line in that block, from the third-letter line on right-hand side of the table

 The codon 5'-ACG-3' codes for the amino acid  Thr (Threonine).