Starch is made up of long chains of glucose, which is a simple sugar. Starch can either be simple linear lines of glucose, like amylose, or it can be a complex molecule with glucose branching off the chain, like amylopectin.
Starch is found in nature in plants. Glucose that is produced by photosynthesis and is not needed right away is stored as starch. Different plants store the starch in different organelles. For example, starch is heavily stored in tubers that people eat from potato plants. If the plant requires energy, it breaks down the starch back into glucose. Similarly, humans can eat starchy fruits and flowers for energy, as the starch can be broken down into glucose.