Unlike carbohydrates , proteins and nucleic acids they aren’t polymers but small molecules, with a molecular weights that range between 100 and 5000, and also vary considerably in polarity, including hydrophobic molecules, like triglycerides or sterol esters, and others more water-soluble like phospholipids or very short-chain fatty acids , the latter completely miscible with water and insoluble in non polar solvents.
The little or absent water-solubility of many of them means that they are subject to special treatments at all stages of their utilization, that is in the course of digestion , absorption , transport, storage and use.
Phospholipids are major components of the plasma membrane, the outermost layer of animal cells. Like fats, they are composed of fatty acid chains attached to a glycerol backbone. Unlike triglycerides, which have three fatty acids, phospholipids have two fatty acids that help form a diacylglycerol. The third carbon of the glycerol backbone is also occupied by a modified phosphate group. However, just a phosphate group attached to a diacylglycerol does not qualify as a phospholipid. This would be considered a phosphatidate (diacylglycerol 3-phosphate), the precursor to phospholipids. To qualify as a phospholipid, the phosphate group should be modified by an alcohol. Phosphatidylcholine and phosphatidylserine are examples of two important phospholipids that are found in plasma membranes.
Sterol lipids, such as cholesterol and its derivatives, are an important component of membrane lipids,  along with the glycerophospholipids and sphingomyelins. The steroids , all derived from the same fused four-ring core structure, have different biological roles as hormones and signaling molecules . The eighteen-carbon (C18) steroids include the estrogen family whereas the C19 steroids comprise the androgens such as testosterone and androsterone . The C21 subclass includes the progestogens as well as the glucocorticoids and mineralocorticoids .  The secosteroids , comprising various forms of vitamin D , are characterized by cleavage of the B ring of the core structure.  Other examples of sterols are the bile acids and their conjugates,  which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver. The plant equivalents are the phytosterols , such as β-sitosterol , stigmasterol , and brassicasterol ; the latter compound is also used as a biomarker for algal growth.  The predominant sterol in fungal cell membranes is ergosterol .