Reference resources are usually encyclopedias, dictionaries, handbooks, manuals and other books that you would refer to when wanting to know a definition of a word or concept, a general overview of a topic, specific information about a certain period of time or event in history.
Using Wikipedia can be a great place to start your research. You can learn about a topic, much like you can in Credo Reference, but you can also find links to other sources. Never cite Wikipedia, but use it as a jumping off point for your research.
For example, look up the author Kate Chopin, who wrote Desire's Baby.
https://en.wikipedia.org/wiki/Kate_Chopin
- you will see all of Kate Chopin's works listed. Check under the References section to see if there is an essay about Desire's Baby. There could also be a book mentioned with a link to the actual book. Use the Reference section as a jumping off point to secondary sources.