TRIE/PREFIX TREE Based Question Editorial Doubt

In the given question:
acoording to the editorial the problem has been solved by the concept of TRAI/PREFIX tree.
but in the editorial it has been asked–" at every node while inserting store 2 extra variables one for the priority and the other for the index of the string with the priority".I am not getting what actually to insert.plz if possible can anyone explain it tom me.
WHAT is “Index” over here