Before you can start to remove grass or level your site, you need to mark a circle that marks the edges of your pool. Most of us can draw a pretty good circle by hand on paper, but marking a 12 or 15 foot circle free-handed is actually quite difficult. The following method should make it quite a bit easier.
First, drive a small post into the ground at the center of your site and tie some twine to it. Measure out the radius of the pool that you purchased (half of the size shown on the box) and cut the string about 8″ – 12″ longer than that dimension. Hold the string and a can of spray paint, and spray the paint on the ground while keeping a steady, light tension on the string. This should create a nearly perfect circle on the ground. You can use this as a guide-line clearing the grass from your pool area. Again, remember that perfection is not required. Clear an area that roughly resembles the shape of your pool, then after the pool is set up, you can replace the grass in any spots where you cleared too much.