The lysosome is a small body or vesicle, which contains enzymes used in digestion, found within the cytoplasm of a eukaryotic cell. These enzymes are reactive enough to break down cellular components, so they are stored within the cytoplasm with a protective membrane that composes a vesicle. So a lysosome is composed of enzymes and a membrane to surround them.
Lysosomes act in three different ways: phagocytosis, endocytosis, and autophagy. Phagocytosis is the process by which a foreign body is engulfed by the cell wall, forming a vacuole. Vesicles can attach to the vaculoe, forming a lysosome, and break the foregin body down. Endocytosis is a process where the cell wall components themselves can be broken down and recycled by a lysosome. Autophagy is the process in which different internal cellular components are contained and degraded, such as worn-out mitochondria. See the links for more info: