Numbering starts in the upper left corner and moves left to right, top to bottom. For example, planting square A1 is the upper left-hand square (1st column, 1st row), while planting square C4 is the square in the 3rd column and the 4th row. I have yet to find a commercially available garden bed with an included feature for marking off planting squares.
Circular raised beds with a path to the center (a slice of the circle cut out) are called keyhole gardens. Often the center has a chimney of sorts built with sticks and then lined with feedbags or grasses that allows water placed at the center to flow out into the soil and reach the plants roots.
Urban gardening is now very popular these days because of food safety awareness, our financial economy, and because we want to be eco-friendly. Just because you only have a garden area that is very small does not mean you cannot use some small raised garden beds on a patio, deck, or back porch for some herbs, vegetables, flowers, or ornamental plants to enjoy.
Each planting square has an address used to identify the square. While the methods for addressing vary, one of the simplest is to use letters for columns and numbers for rows, and the combination of the two identifies the square.