When you interact with an Interaction card using an Item identified by a letter and a number, 2 things can occur:

On the Interaction card, only the letter appears, with no number. This means that any Item with that letter is fine, regardless of the number.

On the Interaction card, a number is specified next to the letter. In this case, you must have used the specific Item with that exact letter and number in order to read the matching paragraph.

You can usually interact with each Interaction card only once, after which it is discarded (note: you can consult the discard pile whenever you want). So, choose carefully which ones to interact with, when, and with which Items. You will find plenty of clues in the game, both in the texts and the illustrations, that will help you figure out what is the best thing to do.