Enter your search terms as you normally would in the search box. In the Search Options below the search box, go to Document Type and select Case Study, then click search.
Do a subject search by typing [case studies] in the search box and selecting SU Subject Terms from the dropdown menu. This will show you all items with case studies as a subject heading.
You can add additional search terms to search for case studies on a topic or use limiters on the results page to narrow your focus.