Step One: Paint the base coat of your choice, you can do two if you like :)
Step Two: Using a cosmetic sponge paint the desired colours, as shown in the second picture.
Step Three: Sponge the colours onto the nails. After each nail make sure to put more nail polish on the sponge.
Step Four: Let dry, then add a top coat or glittery polish if desired.
Do not put too much nail polish on the sponge, just enough for each nail.
You can use as many colours as you want, they can be bold, or blend (like in the top photo).