Setting up a spiral garden is pretty straightforward. Arrange the perimeter of the circle first then gradually fill your way toward the center while building up the spiral. You may want to set up an outline first by using a garden hose first to see how large you want the spiral. I would also advise removing the sod below it or laying a thick layer of cardboard and newspapers to prevent weeds and grass from growing in underneath.
Spiral gardens are a good option if you have a limited amount of space to grow your herbs and vegetables. I don't think this is a good idea for tomatoes, but your spring greens should be happy!