You can use as many colors as you like to do this, but I will demonstrate with two.
Polish your nails with the 'base' color. Allow this to dry for a good 10-15 minutes.
Place a piece or pieces of tape on your nail to create a design.
Polish the section showing with your 'accent' color.
Allow this to dry for about 5 minutes and remove tape.
Apply a top coat, allow it to dry, and you're done. Fun, professional looking nails that are easy to create. :)