API call individually?

Hi there - Newbie here trying to find his way in this no code world! Thx in advance…

Is that possible to call 3rd party APIs per user? What I mean is that, I have a ‘to do app’. When a user adds a new ‘to do’ in the app, I want to create a new card on 'the user’s trello board". I tried to understand the API documentation of yours and I assume I am only allowed to use ‘a master API’ which can create cards on ‘MY trello account’ - not the user’s. Am I right? If so, is there a way for that?

Any help would be fantastic!