The answer is ribosomes.
The ribosome is the molecular machine inside the cell that makes protein from amino acids in a process called translation. It binds to a messenger RNA (mRNA) and reads the information contained in the sequence of bases of the mRNA.
Transfer RNAs (tRNAs) containing amino acids enter the ribosome in a special pocket or binding site, called the acceptor site (A site). Once correctly bound, the ribosome can add the amino acid on the tRNA to the growing protein chain, linking each amino acid to another with pin point accuracy.