You can buy them at pretty much any craft store. The ones I found were Martha Stewart brand and came with a set of 12 colours. There are other brands and sets, so search around a bit. (the how to is below, next to the third picture!: ) )
-First apply one coat of nail polish and then a thicker second coat.
-Sprinkle the beads onto the wet second coat and press them into it. You can put as many beads as you want and as many different colours too!
I didn't use a top coat because I heard that it took the colour out of the beads, but I'm not really sure if that's true or not. I guess it could depend on the topcoat.
Give these nails a try, they're super simple and are reallllly cute! And a little bit weird. : D
(Nailpolish: Essie Exotic Liras, Beads: Martha Stewart Microbeads Garnet and Blue Topaz)