The main function of the ribosome in a cell is to synthesize proteins by translating messenger RNA (mRNA) into polypeptides. Ribosomes are complex molecular machines composed of ribosomal RNA (rRNA) and proteins, and they can be found either free in the cytoplasm or attached to the endoplasmic reticulum. This protein synthesis process is crucial for cellular functions since proteins perform a variety of roles, including acting as enzymes, structural components, and signaling molecules, thereby supporting overall cell activity and metabolism.