Robotic Process Automation uses applications' user interfaces to complete an automation task. It is different than web-based API connector-type automation tools. You can still use an API within your flow if it exists, but you can also automate an app that does not provide an API.
As an example, if it is a web app you are trying to automate, you can create an automation to login into the app, navigate through menus, fill out forms, download PDF files, extract data from the downloaded PDF file, and use that data to create an Excel and mail that Excel to someone.
After creating your automation you can run it at periodic intervals by setting a scheduled flow or you can run a flow that can be triggered by an outside event.