As messenger RNA (mRNA) - red - passes through the ribosome - grey, it causes a protein to be made (synthesised) by joining together various amino acids - green - in a particular order.
A different combination of 3 mRNA bases, also called a triplet, codes for each one of the 20 amino acids. Each triplet in mRNA causes a corresponding transfer RNA (tRNA) molecule - blue - to bring in the appropriate amino acid.
This occurs because the triplet of 3 bases in mRNA, also called a codon, pairs up inside the ribosome with the corresponding 3 bases in tRNA. also called an anticodon.
When the transfer RNA has delivered the amino acid to the growing polypeptide chain, it leaves the ribosome, returns to the cytoplasm and picks up another amino acid.
As the ribosome moves along the mRNA strand, the synthesis process continues until it reaches the stop code which causes amino acid addition to cease. The polypeptide is then released, and it may fold into its final protein structure. The messenger RNA may enter another ribosome and repeat the protein synthesis process, or it may be broken down and its sub-units may be re-used.