The stripes are made with a pointy dotting tool.
To do this you must put a drop of your chosen nail polish on a piece of paper (or something like that) and use this to dip your dotting tool in.
I tried to do this on my left hand too, but the stripes came out too uneven (I'm left handed) so I had to give it up, and my left hand is now just pure black. I won't show you my other hand today beacuse 1) it's just black and b) I broke a nail while bowling last evening :(
Well, have a nice day!