Help me understand this

In this problem what does Two substrings of S are considered different if their positions in S are different mean ??

ps: sorry for dumb title.

I think it means something like this:
Consider string “abab”, the substring “ab” and “ab” are considered different as the first “ab” corresponds to index [1,2] while the second corresponds to [3,4]. I am not sure though :face_with_hand_over_mouth:

yeah but how the index can be same ?