One of my teachers taught me this in a craft activity. Incredibly easy to make, and quite pretty too ;)
Use either paper or an old Christmas card or any old card x)
And my explaining isn't so good so hopefully the pictures help.
It takes either 5 to 10 minutes, once you get it though you can easily do it in five minutes rather than 10...
I'm using a Christmas card, but you can also use colored/patterned paper!
Snip off the cover of your card.
Fold your cover in half.
Cut along the crease.
Get one of the halves and fold that in half.
Get your ruler and draw a line on the outside, make sure it's wide! - But not to wide! ;D (I'm rubbish at explaining >_>)
Now draw steep diagonal lines from the line to the crease.
And they should be very steep and not flat.
Cut along the diagonal lines but don't go past the biiig long line ;D
(Yes, I don't know what to call it >_>)
Open it up after your done!
Hold it so the arrow things face down and then fold each other arrow thing up so its fold one up, miss one, fold one up and the ones you fold up should go under the ones you haven't.
Yay! Your bookmark should end up looking something like this, if not, better!