Ribosomes are cellular organelles that use RNA to produce proteins. RNA is used by ribosomes to link amino acids into chains that fold into three dimensional shapes known as proteins. When ribosomes make proteins from RNA, it is called translation. Protein synthesis (translation) is the primary function of ribosomes.
Ribosomes can be found freely throughout the cell or bound to the endoplasmic reticulum. The structure of ribosomes is composed of protein and RNA.