tRNA molecule bind to the exposed codon of an mRNA strand - bound to a ribosome - if they have the complementary anticodon;
Upon binding, the amino acid attached to the tRNA molecule detaches forming a chemical bond joining onto the polypeptide being constructed;
The ribosome moves 3 bases along the mRNA exposing the next codon (for the next tRNA carrying the next amino acid of the sequence);
The last codon on the mRNA is a stop codon signifying the completion of the polypeptide chain.
This process is called translation.