Chop all the ingredients with a sharp knive until they are very small. I usually do this because I like my bars chunky. You can also throw them into a food processor and process until you get a sticky mass that can be rolled out. If it is too crumbly add a drop of water. Really only a drop until all the ingredients come together.
Roll out into a square about 1cm high, obviously you can make thicker bars but then you will have less bars.