This document provides an introduction to lipids, including their structure and functions. It discusses that lipids are made up of glycerol and fatty acids. Glycerol contains three carbon atoms with hydroxyl groups. Fatty acids contain a hydrocarbon chain with a carboxyl group. Triglycerides are formed through condensation reactions between a glycerol molecule and three fatty acid molecules. Phospholipids contain a phosphate group replacing one of the fatty acids in a triglyceride. Lipids contain both hydrophobic and hydrophilic groups, allowing them to be used in biological structures.