I bought mine for £6.50 from Topshop but you can also get them on Asos. I originally wanted leopard printed ones but they didn't have any so settled for these plain silver wraps.
Application is simple - place the wrap on your finger nail, apply heat from a hairdryer to activate the glue, press down firmly and file off the excess. However it's so fiddly and time consuming. It took me a good 30minutes to do one hand and I managed to burn my cuticles with the heat from my hairdryer :(
I have to say I'm a bit disappointed with the outcome. My thumb, forefinger and middle finger came out so crap and I couldn't smooth out the wrinkles. I think this is because my nail beds are more curved on these fingers than on my ring and little finger which came out great. That's what I'm telling myself anyway!
They didn't last long, about two days? The edges became flappy and I ended up peeling them off because they were irritating me so much. I won't be repurchasing these because they're too much hassle for me. But for special occasions they would be great.