AND - use this when ALL the words must be in your results. This will narrow your results. Example: Shelley AND "Ode to the West Wind"; Percy Bysshe Shelley AND "rhyme scheme"
OR - use this to connect synonyms, when ANY can come back in your results. This will broaden a search. Example: Shelley OR Percy Bysshe Shelley; "rhyme scheme" OR "terza rima"
NOT - use with caution since this will eliminate results with the specified word. NOT Mary Shelley