Find overviews, significant names in the field, citations to basic sources in the field, encyclopedias are a good place to start.
In addition to Wikepedia (which covers all topics, but can be uneven), find specific information in subject encyclopedias online.
Some valuable resources from Feinberg Library for psychology topics....
Encyclopedia Britannica Online
Online version of the Encyclopedia Britannica and Merriam-Webster Dictionary & Thesaurus
Virtual Reference Library
A collection of encyclopedias, almanacs, and specialized reference sources for multidisciplinary research
Composed of high-quality articles from the Columbia Encyclopedia, Sixth Edition
CREDO Reference Collection [Link to overview and features ] Was Xreferplus Reference Collection
Contains over 2 million entries from reference books in all major subjects, 65,000+ images (art, diagrams, maps, and photos), and over 93,000 audio pronunciation files.