There are several methods that have been used to work out the evolutionary relationships of organisms. A feature or thing we can examine or label. It is important that the feature be heritable. Analogous Character Shared resemblance between characters by other means than descent, such as adaptation. This is often called a homoplastic character.
Homologous characters are the fundamental basis of cladistics.
In cladistics we look for characters that we can hypothesis are shared because they were inherited from a common ancestor. The premise is that a species develops a new character and passes that character down to its daughter species. Each of the daughter species then can add new characters, but each adds a different one, since they are now separate species and on their own evolutionary trajectory. This continues to happen through time as more and more species split off. We see in retrospect characters shared between two species.