Create a new document with a transparent background layer. I like to work with lots of space, so I've gone for a 600x600 pixel canvas. Use the Elliptical Marquee Tool make a decently-sized circular selection, holding down the SHIFT key as you drag it out so that it keeps equal proportions. Edit > Fill this circle with a solid black color. Without losing your selection, run Edit > Copy and Edit > Paste to duplicate this circle and move it a little to the left so that the two circles are overlapping a little.