A lick of licorice
Anise and star anise are not the same spice, nor are they related species despite the similar name and flavor profile. They do both contain the organic compound anethole, which gives them their similar licorice flavor.
Fennel is another spice that contains anethole. It is a seed that is often confused with anise—due to its similar flavor profile and also to its similar appearance. Fennel seed is considerably larger and often brighter in color than anise seed. Anise seed, in addition to being smaller, also tends to have a small bit of stem "tail" attached to one end; whereas this happens only occasionally with fennel, it is much more frequent in anise seed.
Since anise seed is more expensive to produce than star anise, star anise has surpassed anise in production for anethole extraction and for commercial use in flavoring food products. Anethole is reputedly multiple times sweeter than sugar with the distinction of having a pleasant flavor at higher concentrations.
Toasting star anise for a minute or two in a dry skillet before using greatly enhances the flavor and fragrance.
Star anise has a powerful flavor, be sure to use it sparingly so that it doesn't overwhelm your dish.
Star anise yields more anethole than anise and has become a source of anise extract. Anise extract features large in liqueurs across the West: Sambuca, pastis, absinthe.