Saving data to user profile versus saving to the app

This one’s probably an obvious one, but somehow I am struggling to sort out the following:

Normally app data is saved to the app for all users when I add new items to my database. This is the case whether I am logged in as a specific user or not.

How can I ensure that I am only saving data for a certain user? For instance, I am trying to determine where the user paused in going through a repeating group (set up to show only 1 row/column at a time) in order to bring them back to that same repeating group item when they resume browsing my page.

Is this possible? And specifically for resuming at the user’s previous position in the repeating group?