An anticodon is a collection of three nucleobases found at one end of a transfer RNA (tRNA) molecule. At the other end of the tRNA is an amino acid to be added to a growing polypeptide chain during the translation of mRNA into protein. See the figure below for an illustration of tRNA structure.
During translation, as shown in the following figure, a ribosome passing down a molecule of mRNA examines one RNA codon at a time. At each step, the ribosome plucks a tRNA molecule from the surrounding cytoplasm whose anticodon is complementary to the present codon. It then adds the tRNA's amino acid to the growing polypeptide. The result is that the RNA codon has been effectively translated into an amino acid, based solely on the bonding property of the codon and anticodon.