every fatty acids has a long hydrocarbon chain (with even amounts of carbons, usually 16 or 18) and a carboxyl group.
glycerol is a 3-carbon molecule with 3 -OH groups.
fatty accids and glycerol can be connected by single or double bonds, depending on if the fatty acid is saturated or unsaturated.
when a lipid forms, the -COOH functional groups of 3 fatty acids react with -OH groups of glycerol.
this leaves 16, 18, or 20 carbons, making a triglyceride 16, 18, or 20 carbons long.
hope this helps!
