The idea behind the card in a box is that it folds up flat and fits nicely into an envelope, in this case an A2.
There are all sorts of videos online on how to make these. This card is going to my niece who is turning 13. I used rolled up dollar bills for the candles but be careful not to use any adhesive on them or they could rip when being taken apart. This was also my first attempt at the card in a box so I hope to be able to make more later on. They are super easy to make with just a few score lines and a few cut lines.