I learnt to do these ages ago, and since then I've kept all my christmas cards. They're great for putting little presents in, like jewellerey. I know its kinda the wrong time f year to upload this project but you could always do the exact same thing with birthday cards too. :) x
First, you gotta measure your card, to make sure its actually square. If its not, just cut a bit off so it is. Then you have to cut it in half down the fold, and get the half that has the front on it. This is your lid, but keep the other half too, for the bottom bit. Draw a big X on the card to find the centre. Then fold each corner up to it and score the folds with a ruler or something.
This bits a little trickier to explain. You have to find the lines you've scored, and fold the edges up so they are level with the lines of your X. Score those folds too.
You should end up with a load of these little squares.
There should be a slightly bigger square right in the middle, which will be the top of your lid. On TWO opposite sides, cut down towards each corner of the bigger square.
Do the same on the other sides, except DONT go all the way to the middle square, or you'll end up cutting bits off. Only go as far as the sticky out triangley bits.
Now you have a kind of net for the box, and you have to make it into a box, which is a little fiddly and triky, but you'll get there.
You may need a teensy bit of glue if your box doesnt want to stay in place, it should look like this.
And this is your lid.
Now get your other half of the card, the one that will say merry christmas or whatever in it. Repeat the exact same steps, but make sure you cut a little bit of the sides of the card this time, so that the lid fits.