There are several classes of molecules that perform different tasks, such as lipids, carbohydrates and proteins. There are some molecules that humans can produce themselves, but others have to be found from different sources, such as food.
Molecules are broken down into types based on their characteristics and broken down even further based on the number of bonds they have. For example, sugars are any molecule that has a certain number of carbon atoms strung together along with a single oxygen atom bonded to it. There are three types of sugar molecules. The monosaccharide is a single sugar molecule. A disaccharide is two single sugar molecules bonded together. A polysaccharide is three or more sugar molecules bonded together.
Another class of molecule is protein, which is essentially any molecule produced through the bonding together of several amino acids. These bonds are called peptide bonds. The cell of every species uses the same 20 amino acids to create proteins, but how many amino acids and the sequence in a protein define its characteristics and traits. There are an infinite combination of these.
Another class of molecule found in the body is lipids, which are oily molecules that do not dissolve in water or evaporate easily. There are various types of lipids, such as fats and oils or triglycerides, phospholipids or diglycerides, cholesterol and even steroids.