Encyclopedias and dictionaries can provide background information and can be used to identify key people, events, and dates which can then be used as search terms for finding additional information. Many also provide a jumpstart on your research by listing related readings.
So why use these instead of Wikipedia? The best practice is to use these in addition to Wikipedia, because unlike Wikipedia, the encyclopedias provided here are written by experts in a particular field, Wikipedia entries could be written by anyone; see the Wikipedia general disclaimer.
If you're looking for some alternatives to Wikipedia, try searching for information in these collections of reference books. You'll be able to check facts and learn context for any number of topics.