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These are sometimes referred to as tree rings. The edging will need to be made of stone, clay, or brick and can be scalloped or straight across the top. You will need to purchase 4 pieces of 14" inside diameter bricks and 6 pieces of 24" inside diameter bricks. Clear an appropriate area for your firepit and then lay out the first two 14" pieces to form a circle. Use three of the 24" to form a larger circle around the first one. You can use a bit of concrete to help the pieces stay together, if you want. Use the remaining pieces to set out the second layer, on top of the first. You can put a layer of concrete between the two stone layers, if you want to. If you use scalloped bricks, put the second layer upside down, so the scalloped edges are touching between the two layers. Fill the gap between the circles with river rocks until the brim is reached. Alternatively, you can fill it most of the way to full and then put down a thinner layer of more aesthetically pleasing rocks, like glass pebbles. Put a small layer of river rocks or other fire-friendly material in the bottom of the pit. Alternatively, you can find a grill bowl with the same diameter (or very slightly larger) as the central circle and place it there. Set up a wood fire in the central pit and enjoy your new fire pit. Put a circular grill surface over the hole to use it as an outdoor cooking pit!
Get curved pieces of garden edging. Lay out the first layer. Lay out the second layer. Fill with rocks. Line the bottom. Light your fire!