The Advanced Search from the Catalog tab gives you many options.
Use the drop down menus on the left to tell Library Search where it should look for your words (in the keyword, title, subject or author fields).
You have two rows, so you can make some complicated searches. For example, the top row could be a title search for all titles containing "introduction" while the bottom row could be a subject search for the exact term of "Nursing". Use the X on the right if you do not want a second line at all.
Use AND when the search results need to have both the criteria from the first line AND the second line. Use OR when you want results that have any of the criteria you listed. You can even specify that you want some criteria to NOT show up in your result list.
The bottom of the search page allows you to narrow your search even further. Choose the format, location, language, or date range of the materials that you would like in your results list.