Wikipedia can be considered a reference source, but, because the content in Wikipedia can be created by anyone, it has not been entirely accepted by the scholarly community as yet. (Traditionally published reference sources are vetted by scholars, generally.) Read Wikipedia articles with a critical eye in order to detect bias.
Wikipedia articles can be very helpful, however, because they often contain links to external content and additional references listed at the end.
Reference books are helpful starting places if you need:
Search collections of reference sources online by keyword: