Homologous organs are organs which are similar in the underlying anatomy but perform different functions, like a human arm and a bat's wing. These homologous organs point towards a common ancestor from which these organisms evolved. These organs are therefore a nice evidence of evolution.
Vestigial structures are often homologous to structures that are functioning normally in other species. Therefore, vestigial structures can be considered evidence for evolution, the process by which beneficial heritable traits arise in populations over an extended period of time.