They work with different people in different ways, depending on the person's personality. Some people are really sensitive to them and can pick up on live messages from them. Others, like me, have personalities that are much less intuitive - I just tend not to pick up spoken messages or sense presences. But the cards provide me with a bridge to the otherworld, and I can make myself receptive to the messages coming through that way. Maybe I don't hear faery voices directly, but I can reflect on and soak up the message of the card I draw that represents the presence of the faery(s) of the moment in my life - I'm receptive. That's the first thing. The other thing is that relating to the faeries impacts on your life, and if you're alert, you can notice some of the changes. This is just as difficult to see, in a way - you have to be monitoring your feelings and attitudes and interactions pretty regularly to see it.
So, if you're sensitive, you can 'read' the source of the message directly, and if you're alert, you can 'read' the expression of it in your life.