getting previous, current, and next data from database

I'm beginner in CI4 and currently learning about database handling.

I want to make a phone display site, where user could select a phone, then check previous and next entry / model.

So I know about getResult() and how to show everything, and I know that getRow(##) could return specific row. There's also getNextRow() and getPreviousRow(), but I can't find the proper way of using it.
I'm not even sure how I could find the "current" index of item I'm browsing. Do I skipped some step on database handling? I can't use cheap trick like "item_ID - 1", because the ID is somewhat mixed up between brand (like Nokia, LG, iPhone, for example).