Reference sources are extremely useful for providing authoritative overviews and background information on a topic. They will give you the terminology and the key names, dates and concepts that can be used when conducting online searches for scholarly articles and books.
Many reference sources also provide extensive bibliographies that list the important and influential scholarship on a given topic.
There are quite a few reference sources available online. Here is a selection:
General and Subject Specific Encyclopedias:
Historical dictionary of the English language (for etymologies)
The library also has quite a few reference sources are available in print. Those with call numbers are available in the Honnold/Mudd Library reference collection (HON REF on the 2nd Level of Multi Tiered Stacks). Browsing the reference shelves in call number ranges PN, PR, and PS will turn up many additional resources.