Reference sources--like dictionaries and subject encyclopedias--provide overviews of topics and descriptions of concepts and ideas. They can also provide definitions, statistics and other details. You can use this type of source to help narrow your research topic, find data to support your thesis and identify keywords and main ideas to use as search terms.
There are a lot of great resources on the web where you can find information about Philosophy. Hover your mouse over the links to find out what they contain. Have fun exploring!