During the adventure you will encounter people, places and animals/monsters that are native to this little part of the "world". While going through the motions, you can, if you so desire, *use* or *activate* one or more cards in order to make things easier to convince/defeat/circumvent/...
You are given absolutely *zero* clues on what cards would be beneficial to use, apart from the link in my/our Gdrive showing all of them. The names and the corresponding drawing should give sufficient clue as to whether or not you want to activate the card.
I will however help you by saying something similar to "You feel the cards glow against your side." indicating that you can choose to activate one or more cards for this 'scene'. Cards can only be activated once, and if you chose the wrong one you obviously receive no benefits, neither at that time or later.