Ahhhh yes, the ancient Chinese philosophy of Taoism. Aside from being a very interesting idea, it gave us the yin-yang (yong) symbol. Recognized the world over. 
So, there are lots of cool things to do with this symbol. What we're gonna create here is a traditional b&w yin-yang. You'll have the ability to do plenty with it later. Let's start! 
Step 1: Let's start with a decent sized canvas, let's say 600 x 600. Make the background transparent. Make sure to turn on your rulers, you're gonna need 'em. View>Rulers (or ctrl + R)
Step 2: Holding down the shift key, create a perfect circle that takes up most the canvas. Fill it with black. If you know about guides, skip the next step.
Step 3: Ok here's where your rulers come in. If you click on the ruler inside the frame and drag into your content area you will get a blue line across your page. Notice it is adjustable! The guides help you to create symetrical and precise images. Very useful all the time.
Step 4: Make sure that snapping is enabled (View>Snap) because it's going to make this tute easy. Drag a vertical guide to the center of your circle. It will snap at the exact center (ah ha!). Drag a horz. line to the very bottom and top of the circle, it will snap. Now drag a horizontal guide to the center. You should have crosshairs in the middle of your circle and one blue line on the top and bottom of the circle. There is a screen capture at the bottom with an example of the important steps.
Step 5: Create a new layer, call it "curves" or something. With your marquee tool select a perfect circle (shift key) starting from the middle horz. line down the bottom one. Fill with white. Now use the move tool to drag your white circle to the dead center of the crosshairs. It will snap in place vertically and horizontally.
Step 6: With the square marquee select half of the white circle (will snap to guide) copy it and then cut it.
Step 7: Make a new layer and paste the other half of the cirlce in. Now drag it into the middle until it snaps in the center (you may have to nudge it over a pixel or two). If you get rid of the guides (ctrl+H) then you should see the same result from step 4, except now with two layers.
Step 8: Repeat steps 6 and 7 for the black circle layer. Your layer menu should look like the capture, and your image should still look like step 4.
Step 9: Drag each half of the small circle to the top and bottom of the large circle respectively. (see screen capture if you're confused). It should now look like a yin-yang without the proper coloring.
Step 10: Load the layer transperancy for your right half of the small circle (DO NOT use the magic wand tool! This will make a jerky cut, and we don't want that!). To do this select your right side layer of the small circle and click on select>load selection. The default is the layer transperancy. Now switch to the right side of the black circle and delete the selection from it. You should have an almost yin yang half. Now repeat for the left side of your circles.
Step 11: Almost there! Traditionaly the right side of the yin yang is white, but a Taoist would tell you it doesn't really matter. However I'm going to stick with tradition. So! Select the right side of the black circle and hit ctrl+I to invert the image now you have one half. Repeat for the other side on the white circle to make it black. Congrats! You now have a Yin Yang! We're not done yet though. Grab a couple more horz. guides and put them in the middle of your small circles. This will give you two more sets of crosshairs in the middle of each yin yang half. Now create a perfect circle on a new layer, fill with white, and position in the middle of the cross hairs in the left (black half). Repeat for the right side, but your new circle black.
All done!! I hope you enjoyed this tute. To my knowledge there isn't a Yin Yang tute out there. So I hope you find mine to be easy. Merge the layers as you see fit. If you keep them apart you can do some cool stuff. I'll make a reply to this tute with an example. Have fun kids! 
Your Yin Yang should be cool! Lao Tzu would be proud!
So, there are lots of cool things to do with this symbol. What we're gonna create here is a traditional b&w yin-yang. You'll have the ability to do plenty with it later. Let's start! Step 1: Let's start with a decent sized canvas, let's say 600 x 600. Make the background transparent. Make sure to turn on your rulers, you're gonna need 'em. View>Rulers (or ctrl + R)
Step 2: Holding down the shift key, create a perfect circle that takes up most the canvas. Fill it with black. If you know about guides, skip the next step.
Step 3: Ok here's where your rulers come in. If you click on the ruler inside the frame and drag into your content area you will get a blue line across your page. Notice it is adjustable! The guides help you to create symetrical and precise images. Very useful all the time.
Step 4: Make sure that snapping is enabled (View>Snap) because it's going to make this tute easy. Drag a vertical guide to the center of your circle. It will snap at the exact center (ah ha!). Drag a horz. line to the very bottom and top of the circle, it will snap. Now drag a horizontal guide to the center. You should have crosshairs in the middle of your circle and one blue line on the top and bottom of the circle. There is a screen capture at the bottom with an example of the important steps.
Step 5: Create a new layer, call it "curves" or something. With your marquee tool select a perfect circle (shift key) starting from the middle horz. line down the bottom one. Fill with white. Now use the move tool to drag your white circle to the dead center of the crosshairs. It will snap in place vertically and horizontally.
Step 6: With the square marquee select half of the white circle (will snap to guide) copy it and then cut it.
Step 7: Make a new layer and paste the other half of the cirlce in. Now drag it into the middle until it snaps in the center (you may have to nudge it over a pixel or two). If you get rid of the guides (ctrl+H) then you should see the same result from step 4, except now with two layers.
Step 8: Repeat steps 6 and 7 for the black circle layer. Your layer menu should look like the capture, and your image should still look like step 4.
Step 9: Drag each half of the small circle to the top and bottom of the large circle respectively. (see screen capture if you're confused). It should now look like a yin-yang without the proper coloring.
Step 10: Load the layer transperancy for your right half of the small circle (DO NOT use the magic wand tool! This will make a jerky cut, and we don't want that!). To do this select your right side layer of the small circle and click on select>load selection. The default is the layer transperancy. Now switch to the right side of the black circle and delete the selection from it. You should have an almost yin yang half. Now repeat for the left side of your circles.
Step 11: Almost there! Traditionaly the right side of the yin yang is white, but a Taoist would tell you it doesn't really matter. However I'm going to stick with tradition. So! Select the right side of the black circle and hit ctrl+I to invert the image now you have one half. Repeat for the other side on the white circle to make it black. Congrats! You now have a Yin Yang! We're not done yet though. Grab a couple more horz. guides and put them in the middle of your small circles. This will give you two more sets of crosshairs in the middle of each yin yang half. Now create a perfect circle on a new layer, fill with white, and position in the middle of the cross hairs in the left (black half). Repeat for the right side, but your new circle black.
All done!! I hope you enjoyed this tute. To my knowledge there isn't a Yin Yang tute out there. So I hope you find mine to be easy. Merge the layers as you see fit. If you keep them apart you can do some cool stuff. I'll make a reply to this tute with an example. Have fun kids!
Your Yin Yang should be cool! Lao Tzu would be proud!