An enzyme-substrate complex is formed when an enzyme binds to its specific substrate, which is the molecule upon which the enzyme acts. This interaction occurs at the enzyme's active site, a specially shaped region that fits the substrate like a key in a lock. The binding of the substrate to the enzyme facilitates a chemical reaction, allowing the substrate to be transformed into products. Once the reaction occurs, the enzyme releases the products and is free to bind with new substrate molecules. This process is crucial in biological systems, as enzymes like amylase and lipase help speed up reactions necessary for life, such as digestion and metabolism.