Homologous structures are structures that we find across different species. They have the same organisation (they have the same parts) but have different functions (they are used for different things).
homologous structures can be used to interpret evolution, because they show that different species share common features which must have been inherited from a common ancestor.
These structures have a different function because different species use these parts for different purposes. This supports evolution by supporting the claim that organisms adapt (change) in response to their environment.
Hope that helps, sorry if unclear