lipid are made up a wide variety of molecules, but they all contain carbon, hydrogen and oxygen with a much higher percentage of carbon and hydrogen molecules than oxygen.
There are three kinds of lipids in living organisms: triglycerides, phospholipids and steroids (hormones).
Triglycerides are made up of a glycerol molecule, with three fatty acid chains attached by ester linkages. Glycerol is an alcohol containing 3 carbon atoms. The fact it is an alcohol means it has an -OH group at one end.
Triglycerides with unsaturated fatty acids (or with relatively long fatty acid chains) have a higher melting point, and so are solids at room temperature. These are known as fats, whereas saturated fatty acids (or with relatively short fatty acid chains) are known as oils and are liquids at room temperature. Plants generally produce oils such as olive or corn oil, and animals produce fats such as butter and lard, but there are exceptions to the rule.