Believe it or not this seemingly impossible thing is made out of only one piece of card, and requires no gluing.
It is actually quite hard to make a place card stand up if you just use a strip of card folded in half, as anyone who has ever been to a conference will testify.
Even the thinest paper will make a rigid sign.
Step 1: Start With a Square of Card
Mark out the square of card s above. I have drawn this in thick pen so that it shows up in the photo.
I have used thin card with fabric glued to both sides.
Step 2: Start With a Square of Card.
Cut in from the side along the three lines to the center line.
Step 3: Folding - This Is the Tricky Bit to Explain
Fold the end flaps in opposite directions.
It helps to score the center line but it is not essential.