This guide from the MIT Libraries explains Boolean operators, keywords versus subject terms, truncation & wildcards, fields, phrases, and stop words.
When you find a really good article or book for your topic (whether or not you have immediate access to the complete item):
AND, OR, and NOT diagrams
(We recommend caution when using NOT. It's easy to throw out the good with the bad.)
Most databases list which Boolean operators are available. "AND" is often implicit if you place terms next to each other. Look for "Search Help" or "Tools" to find details on Boolean operators or other idiosyncracies of that particular database.
SEARCH THE CATALOG (and more)