Subject headings are categories--each standing for a particular event, concept, person, etc.--that allow you to do precise Franklin searches. A subject search for capitalism, for example, will bring you to a long list of subjects that start with capitalism. You can browse through this list to find the specific capitalism-related subject that is most relevant to you.
Here are a small selection of representative Franklin subject searches:
Keyword searches look for search terms anywhere in the record, i.e. the author, subject, title fields, etc. When you find a work of interest, check the full view of the record to see subject headings that can lead to further relevant works.
Try Franklin keyword searches such as:
Finding primary resources on comparative capitalist systems using Franklin
The University of Pennsylvania Libary has many books that either are or contain primary resources about economic history.