NOT - tree not cats retrieves items containing one word, tree, but not containing the other word, cats. Not limits search results. Usually the words will be in the same sentence. Parentheses - Keeps the words in a phrase together and help organize the priority of the components of the search statement. Truncation - allows searcher to retrieve longer forms of a word.
Many databases require that a symbol is input at the end of the word.
Read the Help for each database for the symbol it uses.