Depending on your topic and your own knowledge about it, you may want to find an overview.
Encyclopedias are usually excellent sources for overviews.
Use these links, or ask a reference librarian for help. Use Inter-Library Loan to borrow something from another library. To find things in non-PALS libraries, go to our Books and Media page. Be sure to ask a reference librarian if you need assistance. You might find it helpful to have your internet browser open in three windows.