API Calls: How do we find the end point for websites and fields on webpages?

Can API call be used to feed information from an inventory file to, say, a three-page online form? I am trying to automate a process that logs in to a portal, fills a 3-page online application form, and then uploads a pdf file to the portal.

Can all of this be done using API call in Uipath? If yes, then how would we identify fields, buttons, combo boxes, etc.?

First, you need to get the API documentation endpoints for the respective site/sites.

Then, test the API calls in Postman, and in the end, use the HTTP Request activity to automate in UiPath Studio.

An API wouldn’t use fields, combo boxes, etc. That is the UI or User Interface. An API would just have a strict set of rules where you’d pass information to it, then receive information back. You’d need the documentation for the API to know those rules.