REST APIs provide access to resources (data entities) via URI paths. You can visit the Ansible Tower REST API in a web browser at:
http://<Tower server name>/api/
Clicking on various links in the API allows you to explore related resources.
Clicking on the next to the page name (toward the top of the screen) for an API endpoint gives you documentation on the access methods for that particular API endpoint and what data is returned when using those methods.
You can also use PUT and POST verbs on the specific API pages by formatting JSON in the various text fields.