Complex sentence: There are 64 different codons but only 20 different translated amino acids and 3 stop codons, allowing most amino acids to be encoded by more than one codon.
Split into simpler sentences: There are 64 different codons but only 20 different translated amino acids plus 3 stop codons. The overabundance in the number of codons allows many amino acids to be encoded by more than one codon.