Keywords are the words you can use to search that can be phrases or words that are, for the most part, in natural language. Subject headings are different. Subject headings function like tags to link together books, articles, or items that are similar in their content. These often do NOT reflect natural language.
For a topic on indigeneity and literature, you could do a quick keyword search for Indians and literature, indigenous peoples and literature, or name a specific indigenous group (i.e., the Navajo) and literature.
It can be more effective to browse the assigned subject headings for related works to see what other ways books that are relevant to your area of study might be categorized. For example, this book:
Has the following subject headings:
Some of these will be more effective than others in leading you to similar books in the library. Note that references to groups, like "Indians," does not reflect the current preferred nomenclature for groups of people - and that will be true across ethnic groups and peoples.